KR100839074B1 - 3-phase pwm inverter system using single dc-link current sensor - Google Patents

Abstract

A 3-phase PWM(Pulse Width Modulation) inverter system using a single current sensor is provided to improve a pulsation phenomenon of a load current by changing a voltage modulation process which is applied to recover a 3-phase current. A 3-phase PWM inverter system using a single current sensor includes a single current sensor(4), and a controller(7). The single current sensor detects a DC link current of the inverter. The controller outputs a reference voltage vector which is a reference of a load control. An output reference voltage vector determines an initial sector included in a voltage vector plane. The controller determines a sector where the reference voltage vector is included by applying a hysteresis according to a moving direction of the reference voltage vector after determining the initial sector. The controller determines an amended voltage vector which is injected to recover a phase-current in a dead zone where a maintaining time of a PWM switching is smaller than a specific time in the voltage vector plane based on the sector determined by the hysteresis. The controller amends the reference voltage vector by modulating the reference voltage vector based on the determined amended voltage vector. The controller outputs the amended reference voltage vector to the inverter, and controls an operation for recovering a 3-phase current based on a DC link current which is detected through the single current sensor.

Description

3-Phase PWM inverter system using single DC-link current sensor}

1 is a diagram illustrating a dead zone in which three-phase current recovery is impossible in a general voltage vector plane.

2 is a diagram illustrating a method of modulating and compensating a reference voltage for restoring three-phase current.

3 is a control block diagram of a three-phase PWM inverter system using a single current sensor in accordance with an embodiment of the present invention.

4 is a block diagram for phase current acquisition in a three-phase PWM interleaver system using a single current sensor according to an embodiment of the present invention.

5 is a diagram illustrating a region of a sector using hysteresis in the voltage vector plane.

6 shows a method of determining a sector using hysteresis.

7 is a diagram illustrating a method of determining the size of a correction voltage vector.

8 is a diagram illustrating another example of FIG. 7.

9 is a diagram illustrating another example of FIG. 7.

* Description of the symbols for the main functions of the drawings *

1: DC link stage 2: inverter

3: Y-connected 3-phase load 4: Current sensor

5: Analog / Digital Converter 6: Inverter Gate Signal Generator

7: controller

The present invention relates to a three-phase PWM inverter system using a single current sensor, and more particularly, in a system for restoring a phase current value using a single current sensor, phase current recovery can be performed by injecting a specific voltage in an area where phase current recovery is impossible. The present invention relates to a three-phase PWM inverter system using a single current sensor that can reduce the current pulsation or noise generated when the voltage injection method is changed.

In general, a three-phase PWM inverter system using a single current sensor installs a single current sensor in a DC-link and applies a phase current (Iu, Iv, Iw) applied to the load from the current measured from the single current sensor. Restore to control the load.

In the Space Vector PWM (SVWWM) scheme, there are up to two switching states that can measure phase current through the DC-link current during the PWM half cycle. In addition, different currents are observed in each switching state. If the current information of two different phases can be found in two switching states, the current information of all three phases can be obtained from the relation of iu + iv + iw = 0 of the Y-connected load. However, in order to measure the exact current value of two different phases, the two switching states must be maintained for a certain period of time. The hexagonal dark gray region at the center of the voltage vector plane shown in FIG. 1 shows the shape of a section in which the load control reference cannot be maintained for the time required for two switching states when the reference voltage vector is located in the region. . In other words, in this section, the current SVPWM switching type corresponding to the reference voltage does not properly obtain two-phase current information. This area becomes wider so that the holding time of the switch state required for current recovery can be long. This zone is called a dead zone.

When the reference voltage is located in the dead zone to obtain two different phase current information in the dead zone, the reference voltage vector adds the correction voltage vector during the first half of the PWM period and the same magnitude and the same direction as the correction voltage vector for the remaining half period. The compensation voltage vector is added to change the PWM switching waveform. At this time, the average value of the voltage in the PWM period is constant and remains the same as the reference voltage vector. On the other hand, the correction voltage vector is selected as the vector of the minimum distance connecting the dead zone boundary from the reference voltage. As shown in FIG. 2, when the reference voltage is A (or B, C), the correction voltage vector is a (or b, c) and the compensation voltage vector is a '(or b', c '). Meanwhile, the correction voltage vector and the compensation voltage vector for one PWM period are referred to as injection voltage vectors.

When the reference voltage is corrected and compensated, a sudden change occurs in the injection voltage vector pattern when the reference voltage crosses a sector boundary shown in FIG. 1. This phenomenon is undesirable because it causes a relatively large current pulsation. Therefore, in the dead zones belonging to sectors 2, 4, and 6, the pattern of the injection voltage is made constant by adding the compensation voltage vector to the reference voltage vector during the first half of the PWM period and the correction voltage vector to the reference voltage vector for the remaining half of the PWM period. The same process is followed for the remaining sectors. In the case of Y-wire balanced load, the phase voltages vu, vv, and vw satisfy the relationship of vu + vv + vw = 0 as well as the phase currents. That is, in the three-dimensional Cartesian coordinate system, (vu, vv, vw) is located on the plane x + y + z = 0, and since the origin is also on the same plane, all voltage vectors (vu vv vw) are also on the plane x + y + z = 0. Is put on. This plane is called a voltage vector plane, and V1 to V6 in Fig. 2 show the voltage vector generated in the switching state of the PWM inverter on the voltage vector plane. Each sector is an area between V1 and V6 as shown in FIG.

When current control is performed using the current information obtained by the above method, current measurement noise is reflected in the reference voltage through the controller. The reference voltage is determined through a closed control loop, such as a current control loop, in which the sensing noise of the feedback signal, etc., is presented to the reference voltage through the controller. That is, the reference voltage includes high frequency pulsation, and when the low frequency component of the reference voltage passes through the sector, the sector to which the reference voltage belongs is determined by alternating between the previous sector and the moving sector by the high frequency pulsation of the reference voltage. . That is, the high frequency pulsation is included in the reference voltage. When the reference voltage is near an arbitrary sector boundary of the voltage vector plane shown in FIG. 2, the sector may be changed instantaneously several times due to this pulsation component. This phenomenon leads to pulsations of current and causes noise, especially in the dark gray hexagonal region of FIG. 1.

SUMMARY OF THE INVENTION The present invention solves the above problems, and an object of the present invention is to provide a three-phase PWM inverter system using a single current sensor that can reduce the current pulsation and noise that may be caused by the sector change of the reference voltage vector. will be.

A three-phase PWM inverter system using a single current sensor of the present invention for achieving the above object is a three-phase PWM inverter system for driving a load using a three-phase PWM inverter, for detecting the DC link current of the interleaver Outputs a single current sensor and a reference voltage vector that is a reference for load control, determines the sector to which the output reference voltage vector belongs in the voltage vector plane, and maintains PWM switching in the voltage vector plane based on the determined sector. A modified voltage vector is injected to allow phase current recovery in a dead zone where time is less than a specific time, and the reference voltage vector is modulated by using the determined modified voltage vector to correct the reference voltage vector. Output the voltage vector to the inverter, and using the DC link current sensed by the single current sensor And a controller for controlling the operation of restoring the three-phase current.

The controller is characterized in that the sector to which the reference voltage vector belongs is determined by hysteresis according to the moving direction of the reference voltage vector.

When the reference voltage vector is located in the dead zone, the controller determines a minimum voltage vector connecting the dead zone boundary from the reference voltage vector as a correction voltage vector, and when the reference voltage is located outside the dead zone, The correction voltage vector is determined as zero.

The boundary of the dead zone is a boundary of the dead zone in the sector to which the reference voltage vector belongs.

The controller is characterized in that when the reference voltage vector is modulated, the average voltage vector is equal to the sum of the reference voltage vector and the correction voltage vector in the first half period of the PWM and the difference in the remaining half periods.

The controller is characterized in that when the reference voltage vector is modulated, the average voltage vector is equal to the difference between the reference voltage vector and the correction voltage vector in the first half period of the PWM and equals the sum in the remaining half periods.

When the controller modulates the reference voltage vector, the controller selects an average voltage vector of each half period by reversing the order of the half periods in which the correction voltage vector is added to and subtracted from the reference voltage vector at even and odd sectors in the voltage vector plane. It is characterized by determining.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

Figure 3 shows a control block diagram of a three-phase PWM inverter system using a single current sensor according to an embodiment of the present invention. Referring to the drawings, a three-phase PWM inverter system using a single current sensor of the present invention is applied to the DC link stage 1 and the inverter 2 for receiving the rectified voltage of the DC link stage 1 to the AC power source (2). A Y-connected three-phase load (3) receiving the output voltage of the inverter (2), a current sensor (4) detecting current flowing through the DC link stage (1), and detected by the current sensor An analog / digital converter 5 for converting an analog signal into a digital signal, an inverter gate signal generator for controlling the inverter 2, and a controller 7 for implementing an overall control algorithm. It is made to include.

4 is a block diagram for phase current acquisition in a three-phase PWM interleaver system using a single current sensor according to an embodiment of the present invention. Referring to the drawings, the three-phase PWM inverter (e) capable of measuring the DC-link current and the information of the three-phase current (iu, iv, iw) of the load with respect to the Y-connected load (g) It consists of a current recovery unit f for obtaining the P, a correction voltage determination algorithm c in the non-recoverable region, and a smooth change algorithms a and b of injection voltage for reducing current pulsation.

Referring to FIGS. 3 and 4, the operation of the controller 7 will be described. The controller 7 includes a process of determining a sector using hysteresis, a correction voltage vector determination process, a voltage modulation process, a low pass filtering process, Perform phase recovery of load.

Looking at the process of determining the sector using the hysteresis of the controller 7, first, it is determined which sector on the voltage vector plane a given reference voltage vector (voltage command vector) belongs. If hysteresis is not used, the sectors define sectors 3, 4, 5, and 6 in acute angle region between voltage vectors V1 and V2, sector 2 in acute angle region between V2 and V3 in FIG. do. This is the traditional method. After the first sector determination, hysteresis is applied to the change of the sector. In this case, the boundary between the sectors is changed in two ways according to the movement path of the reference voltage, and is indicated by the dotted red line and the dotted blue line in FIG. 5.

6 shows a method of applying hysteresis between two adjacent sectors (vertical axis). Where the horizontal axis represents the 'signed distance' from the voltage vectors Vi, i = 1,2, ..., 6 adjacent to the reference voltage, and the sign is in the positive and counterclockwise directions when Vi is located in the time direction. Negative representation of the location. And the magnitude is defined as the distance between Vi and the reference voltage. Existing sector change occurs at a distance of 0, but when hysteresis is applied, as shown in FIG. 6, at two positions near a distance of 0 according to the moving direction of the reference voltage. The same color among the red and blue colors in FIG. 6 indicates movement in the same sector.

A detailed sector determination operation is as follows.

Step 1: Determine the sector according to the definition of the sector without hysteresis for the given reference voltage vector. Go to step 3.

Step 2: If the sector of the previous reference voltage vector is in the red region, the sector is changed when the current reference voltage vector moves in the clockwise direction and crosses the red line in FIG. 5 compared to the previous reference voltage vector. In addition, when the sector of the previous reference voltage vector is the blue region, the current reference voltage vector is moved in the counterclockwise direction compared to the previous reference voltage vector, and the sector is changed when crossing the blue line of FIG. 5. Go to step 3.

Step 3: After one sample go to step 2.

In addition, referring to the process of determining the modified voltage vector of the controller 7, when the reference voltage is located in the inner region of the regular hexagon shown in dark gray in the voltage vector plane of FIG. 5, the reference voltage among the vertices of the regular hexagon shown in dark gray is shown. When the voltage vector corresponding to the vertex closest to the vector V * is Vp, the correction voltage vector is determined as Vp-V *. On the other hand, when the reference voltage is located in the outer region of the regular hexagon shown in dark gray of Figure 5, one of the methods of Figures 7 to 9 can be used to determine the magnitude of the correction voltage. In each figure, the same color among the red and blue colors represents the movement within the same sector.

7 is a method having a characteristic of minimum voltage injection in sector division using hysteresis. That is, the correction voltage vector is selected as the vector of the minimum distance connecting the dead zone boundary from the reference voltage. The boundary of the dead zone means a boundary within a sector to which the reference voltage belongs.

Vmin in FIG. 7 is the distance to the voltage vectors Vi, i = 1, 2 ... 6 and the dead-zones adjacent thereto. In the outer region of the regular hexagon shown in dark gray in FIG. 5, Vmin is constant because Vi and the adjacent dead zone are parallel to each other.

8 and 9 are methods of introducing hysteresis to voltage injection, respectively. The gray area in each figure is the hysteresis region. Here, the magnitude of the correction voltage is determined by a combination of arrow movements shown in red or blue drawn inside the gray area. In other words, when the 'signed distance' on the horizontal axis is near to the origin, the correction voltage is determined according to the arrow movement shown in the figure. On the other hand, the direction of the correction voltage is a direction perpendicular to the voltage vector Vi corresponding to the distance 0, and if the 'signed distance' is positive, the clockwise direction from Vi, and counterclockwise from Vi if it is negative. In the case of using the method of FIGS. 8 and 9, when the (reference voltage vector ± modified voltage vector) is located in the dead zone, the method described above is replaced with the minimum voltage injection method (FIG. 7).

In addition, referring to the voltage modulation process of the controller 7, the voltage is modulated using the concept of the correction voltage vector and SVPWM determined in the correction voltage vector determination process. In order to make the voltage average value equal to the reference voltage vector in the PWM period, the voltage average during the half cycle of the PWM is the vector of the reference voltage vector plus the correction voltage vector. Let be a vector minus. On each half cycle, the switching pattern is formed in the same way as SVPWM. In addition, the position of the half period to which the correction voltage vector is added may be fixed at the front or the rear of the PWM period and subtracted from the remaining half period. However, in this case, since the current pulsation may be induced as described above, the order of half cycle in which the correction voltage vector is added and subtracted in the even and odd sectors is applied in reverse order.

In addition, referring to the low pass filtering process of the controller 7, the current information of the restored load is filtered using a low pass filter and used in the controller. The lower bandwidth of the low pass filter has the effect of eliminating high frequency pulsation at the reference voltage, but the delay of the current measurement causes the current control performance to be in conflict with each other, thus requiring proper bandwidth selection of the low pass filter.

In addition, looking at the load phase current restoration process of the controller 7, the load phase current restoration of the load is restored in the same manner as the related art operation described above, together with the above method.

As described in detail above, according to the present invention, in the three-phase PWM inverter system using a single current sensor to change the voltage modulation scheme applied to restore the three-phase current during load control to improve the pulsation phenomenon appearing in the load current It can be effective.

In addition, according to the present invention, even if a single current sensor is applied to secure the price competitiveness of the product can be suppressed noise and vibration can be extended to the product that noise and vibration suppression is important.

Claims (7)

In a three-phase PWM inverter system for driving a load using a three-phase PWM inverter, A single current sensor for detecting a DC link current of the interleaver; A reference voltage vector, which is a reference for load control, is output, and the output reference voltage vector determines the first sector belonging to the voltage vector plane, and after the first sector is determined, the change of the sector depends on the direction of movement of the reference voltage vector. The hysteresis is applied to determine the sector to which the reference voltage vector belongs, and based on the sector determined by the hysteresis, the implantation is performed to restore the phase current in the dead zone where the PWM switching duration is less than a specific time in the voltage vector plane. Determine a corrected voltage vector, modulate the reference voltage vector using the determined corrected voltage vector, modify the reference voltage vector, output the modified reference voltage vector to the inverter, and detect the detected current through the single current sensor. Controlling the Restoration of Three-Phase Current Using DC Link Current Three-phase PWM inverter system with a single current sensor, characterized in that it comprises a controller. delete The method of claim 2, wherein when the reference voltage vector is located in a dead zone, the controller determines a vector of the minimum distance connecting the dead zone boundary from the reference voltage vector as a modified voltage vector, and the reference voltage is a dead zone. Three-phase PWM inverter system using a single current sensor, characterized in that the correction voltage vector is determined to be zero when located outside. 4. The three-phase PWM inverter system using a single current sensor according to claim 3, wherein the boundary of the dead zone is a boundary of a dead zone in a sector to which the reference voltage vector belongs. The method of claim 1, wherein the controller, when modulating the reference voltage vector, makes the average voltage vector equal to the sum of the reference voltage vector and the correction voltage vector in the first half period of PWM and the difference in the remaining half periods. 3-phase PWM inverter system using a single current sensor. The method of claim 1, wherein the controller, when modulating the reference voltage vector, makes the average voltage vector equal to the difference between the reference voltage vector and the correction voltage vector in the first half period of the PWM and equals the sum in the remaining half periods. 3-phase PWM inverter system using a single current sensor. 2. The method of claim 1, wherein the controller reverses the order of half periods in which the correction voltage vector is added to and subtracted from the reference voltage vector in the even and odd sectors in the voltage vector plane during modulation of the reference voltage vector. A three-phase PWM inverter system using a single current sensor, characterized by determining the average voltage vector of each half cycle.

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