A semi-controlled open-winding permanent magnet synchronous generator system and a control method thereof

Abstract

The application discloses a semi-controlled open-winding permanent magnet synchronous generator system and a control method thereof, and relates to the technical field of motor drive topology and control. The system comprises: the AC ends of a first converter and a second converter are connected to the two sides of a stator winding of an open-winding permanent magnet synchronous generator; each phase bridge arm in the first converter comprises two series-connected fully-controlled switches with freewheeling diodes; each phase bridge arm in the second converter comprises two series-connected diodes with a small-power fully-controlled switch in reverse parallel connection; wherein the rated voltage and the rated current of the fully-controlled switch and the diode are equal; the rated voltage of the small-power fully-controlled switch is equal to that of the diode, and the rated current is less than 1 / 5 of the rated current of the diode. The semi-controlled open-winding permanent magnet synchronous generator system combined with the control method can weaken the influence of current sampling error and delay, improve zero sequence compensation capability, and further, can completely eliminate the excessively long current zero-crossing duration in the prior art and inhibit harmonic current.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of motor drive topology and control technology, in particular to a semi-controlled open-winding permanent magnet synchronous generator system and a control method thereof. BACKGROUND

[0002] Permanent magnet synchronous generators are widely used in wind power systems due to their high power density and high reliability. Open-winding structure is attracting attention in medium-voltage high-power application fields due to its advantages such as multi-level power supply capability, strong fault tolerance, and flexible control. With the continuous growth of the demand for high power and large capacity in wind power systems, the integration of permanent magnet synchronous generators and open-winding structure shows significant potential. However, the traditional open-winding system requires a large number of fully controlled switching devices, resulting in a significant increase in the cost of the open-winding system. Therefore, a semi-controlled open-winding permanent magnet synchronous generator system emerges as the times require, which realizes system cost optimization by deploying fully controlled converters and diode rectifiers on both sides of the generator.

[0003] Although the semi-controlled open-winding permanent magnet synchronous generator system (hereinafter referred to as the system) has the advantage of reducing cost, the problem of long current zero-crossing duration seriously restricts the performance of the system, and the root cause of this problem lies in the fact that the output voltage of the diode rectifier in the semi-controlled system is only determined by the current direction. In the current zero-crossing region, i.e. the interval adjacent to the zero-crossing point of the phase current, the system often appears modulation misalignment and over-modulation phenomena. SUMMARY

[0004] To suppress the harmonic current caused by modulation misalignment or over-modulation, the current zero-crossing region needs to be converted into a controllable region. Therefore, in the first aspect, the present application reversely connects small-power fully controlled switching devices in parallel to the diodes of each phase of the diode rectifier, so that the voltage vector output by the improved converter can no longer be determined only by the current direction in the current zero-crossing region. The newly added small-power fully controlled switching devices only need to act in the current zero-crossing region, and the current they carry is extremely low, so the additional cost is negligible compared to the original devices of the system, especially for high-power systems.

[0005] Specifically, the present application provides a semi-controlled open-winding permanent magnet synchronous generator system, and the technical solution is as follows:

[0006] The system comprises a first converter, an open-winding permanent magnet synchronous generator, and a second converter.

[0007] The AC terminals of the first converter and the second converter are respectively connected to the two sides of the stator winding of the open-winding permanent magnet synchronous generator.

[0008] The first converter comprises 3-phase bridge arms, and each phase bridge arm comprises 2 fully controlled switches with freewheeling diodes connected in series.

[0009] The second converter comprises 3-phase bridge arms, each of which comprises 2 diodes connected in series; each of the diodes is connected in antiparallel with a small-power fully-controlled switch with a freewheeling diode;

[0010] wherein,

[0011] V 1= V 2= V 3; I 1= I 2≥5 I 3;

[0012] wherein, V 1、 V 2 and V 3 are the rated voltages of the fully-controlled switch, the diode and the small-power fully-controlled switch, respectively; I 1、 I 2 and I 3 are the rated currents of the fully-controlled switch, the diode and the small-power fully-controlled switch, respectively.

[0013] In a second aspect, the application further provides a control method of the semi-controlled open-winding permanent magnet synchronous generator system, and the technical scheme is as follows:

[0014] The control method comprises the control method in the current zero-crossing region, and the control method is specifically as follows:

[0015] A. The control method of the first converter comprises the following steps:

[0016] Step S1: collecting three-phase currents of the semi-controlled open-winding permanent magnet synchronous generator system i a 、 i b 、 i c After that, based on the rotor electric angle θ e Through coordinate transformation, the dq axis current d under the i axis is obtained d and the q axis current i q ;

[0017] Step S2: calculating the difference Δ d between the i axis current d and the d axis reference current i d * i d , q axis current iq With q Axis reference current i q * Difference Δ i q ; wherein, i d * =0;

[0018] Difference Δ i d and Difference Δ i q respectively, PI control processing is performed to obtain d Axis reference voltage u d * and q Axis reference voltage u q * ;

[0019] Step S3: based on the rotor electric angle θ e respectively, the d Axis reference voltage u d * and q Axis reference voltage u q * are converted to αβ Coordinate system to obtain α Axis reference voltage u α * and β Axis reference voltage u β * ;

[0020] Step S4: calculate α Axis reference voltage u α * and reference voltage u α2 * , obtain the α Axis reference voltage u α1 * ; calculate β Axis reference voltage u β * and reference voltage u β2 * , obtain theβ axis reference voltage u β1 * ; wherein the reference voltage u α2 * and the reference voltage u β2 * are output voltage vectors of the second converter respectively V ref2 α axis reference voltage and β axis reference voltage;

[0021] Step S5: performing space vector modulation on the α axis reference voltage u α1 * and the β axis reference voltage u β1 * to obtain a first control signal for controlling the full-controlled switches in the first converter;

[0022] B. A control method of the second converter, comprising:

[0023] performing space vector modulation on the reference voltage u α2 * and the reference voltage u β2 * to obtain a second control signal for controlling two small-power full-controlled switches of corresponding phases in the second converter; meanwhile, the small-power full-controlled switches of the remaining phases are in an off state.

[0024] Compared with the prior art, the technical solution provided by the application introduces full-controlled switches to make the output voltage vector of the second converter no longer determined by the current direction, which can weaken the adverse effects of current sampling errors and delays, and improve the zero sequence compensation capability of the half-controlled open-winding permanent magnet synchronous generator system. Further, the excessively long current zero-crossing duration caused by the uncontrollable output voltage of the diode rectifier in the prior art can be completely eliminated, and the suppression of harmonic currents can be realized. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Fig. 1 is a topological structure diagram of an isolated bus feeding half-controlled open-winding permanent magnet synchronous generator system according to the application.

[0026] Figure 2 Fig. 2 is a voltage space vector diagram of the first converter in the application.

[0027] Figure 3 ​The voltage space vector diagram of the second converter in the application.

[0028] Figure 4 The control block diagram of the topology proposed in the application in the current zero-crossing region outside.

[0029] Figure 5 The control block diagram of the topology proposed in the application in the current zero-crossing region inside.

[0030] Figure 6 The current zero-crossing region diagram of the three-phase current in the application.

[0031] Figure 7 The topology structure diagram of the half-controlled open-winding permanent magnet synchronous generator system with common bus feeding proposed in the application.

[0032] Figure 8 The modulatable range diagram of the first converter when the system adopts the typical control method in the current zero-crossing region of the B-phase current.

[0033] Figure 9 The modulatable range diagram of the first converter when the system adopts the control method provided in the application in the current zero-crossing region of the B-phase current. DETAILED DESCRIPTION

[0034] Hereinafter, the technical solutions provided in the application will be further elaborated in detail in combination with the drawings.

[0035] As shown in Figure 1 , the topology structure of the improved half-controlled open-winding permanent magnet synchronous generator system proposed in the application. The first converter is composed of full-controlled switches with freewheeling diodes, and the second converter is composed of diodes with small-power full-controlled switches in anti-parallel connection. U dc1 is the DC bus voltage amplitude on the side of the first converter, U dc2 is the DC bus voltage amplitude on the side of the second converter.

[0036] wherein,

[0037] V 1= V 2= V 3; I 1= I 2≥5 I 3;

[0038] wherein, V 1、 V 2 and V 3 are the rated voltages of the full-controlled switch, the diode and the small-power full-controlled switch respectively; I 1、 I 2 andI 3 are the rated currents of the full controlled switch, diode and small power full controlled switch respectively. Therefore, the small power full controlled switch is only used to deal with the current with 1 / 5 amplitude and below, which is suitable for dealing with the current in the zero-crossing region.

[0039] As shown in Figure 2 , the eight output vectors of the first converter can be represented by 000, 001, 010, 011, 100, 101, 110 and 111. It should be noted that "1" represents that the upper switch of the corresponding phase arm is turned on and the lower switch is turned off, and the output is high level; "0" represents that the upper switch of the corresponding phase arm is turned off and the lower switch is turned on, and the output is low level.

[0040] The direction of the current flowing into the second converter is positive. As shown in Table 1, outside the current zero-crossing region, the output voltage vector of the second converter is only determined by the direction of the three-phase current i a , i b and i c . Inside the current zero-crossing region, the output voltage vector of the second converter is no longer determined only by the direction of the three-phase current i a , i b and i c , but also can be synthesized by the two adjacent active vectors of the second converter. Among them, as shown in Figure 3 , the vector space of the second converter includes active vectors OA, OB, OC, OD, OE and OF.

[0041] Table 1 Voltage vector-corresponding diagram

[0042] .

[0043] Among them, u α2 and u β2 are the projections of the output voltage vector V ref2 of the second converter on the αβ axis, that is, the V axis component and the α axis component of the output voltage vector β ref2 .

[0044] The system control proposed in the present application is as shown in Figure 4 and Figure 5 , wherein Figure 4 is the system control block diagram outside the current zero-crossing region, Figure 5The system control block diagram in the current zero crossing area is shown in Figure 2. d Axis current control strategy, d Axis reference current i d * = 0, and set q Axis reference current i q * ; Real-time collection of three-phase current through current sensor i a 、 i b 、 i c , and based on the rotor electrical angle θ e Obtained by coordinate transformation dq Under the coordinates d Shaft current i d and q Shaft current i q .Will d Shaft current i d and d Axis reference current i d * Make the difference and get the difference Δ i d ;Will q Shaft current i q and q Axis reference current i q * Make the difference and get the difference Δ i q . The difference Δ i d Sum difference Δ i q As the input of the proportional-integral controller (PI) to obtain d Axis reference voltage u d * and q Axis reference voltage u q * . Get the rotor electrical angle θ e Then, through coordinate transformation dq In the coordinate system d Axis reference voltage u d * andq Axis reference voltage u q * Convert to αβ Get in the coordinate system α Axis reference voltage u α * and β Axis reference voltage u β * .like Figure 4 As shown, outside the current zero-crossing region (i.e., the region from positive current to negative current or from negative current to positive current), the voltage vector output by the second converter at this time is determined by the direction of the three-phase current collected by the current sensor and the output voltage vector is obtained according to Table 1. V ref2 of α Axis component u α2 and β Axis component u β2 Due to the double-end feeding characteristics of the open-winding permanent magnet synchronous generator, its reference voltage V ref The calculation method is as follows:

[0045] ;

[0046] Where, V ref1 is the reference voltage vector of the first converter.

[0047] Therefore, the first converter can be calculated αβ In the coordinate system α Axis reference voltage u α1 * and β Axis reference voltage u β1 * , the formula is as follows:

[0048] ;

[0049] .

[0050] Then, through space vector modulation, a modulated wave is output to drive the first converter. This output control signal controls each fully-controlled switch, achieving modulation of the first converter. Outside the current zero-crossing region, the second converter outputs the corresponding voltage according to Table 1, relying solely on the three-phase current direction. At this point, all low-power fully-controlled switches on the second converter are in the off state.

[0051] To realize the stable switching of the two modulation strategies at the boundary of the current zero-crossing region, the upper and lower limits of the current zero-crossing region need to be set by comprehensively considering the current size and the current zero-crossing duration when the system is working, so as to ensure that the current zero-crossing regions of the phase currents do not affect each other, and at the same time ensure that the current zero-crossing region can contain the entire current zero-crossing duration to eliminate the harmonic current brought by it.

[0052] As shown in Figure 6 , the upper and lower limits of the current zero-crossing region are both provided with hysteresis to ensure that the control method used in the current zero-crossing region and the control method used outside the current zero-crossing region will not be mis-switched. When the phase current is greater than the upper limit of the lower boundary hysteresis of the phase current zero-crossing region for the first time- I L- , the phase current enters the current zero-crossing region. In this case, unless the phase current is lower than the lower limit of the lower boundary hysteresis- I L+ or higher than the upper limit of the upper boundary hysteresis I L+ , the phase current will not leave the current zero-crossing region; correspondingly, when the phase current is lower than the lower limit of the upper boundary hysteresis for the first time- I L- , the current enters the current zero-crossing region; in this case, unless the phase current is higher than the upper limit of the upper boundary hysteresis or lower than the lower limit of the lower boundary hysteresis- I L+ , the phase current will not leave the current zero-crossing region. I L+

[0053] , the amplitude of the hysteresis is 10% to 20% of the amplitude of the zero-crossing region, and the specific proportion can be adaptively adjusted by the technical personnel according to the stable state of the system.

[0054] For the demarcation of the upper and lower boundaries of the zero-crossing region, it needs to be adjusted synchronously according to the difference of the sampling error and the power factor under the condition of the common bus. After the introduction of the hysteresis, the upper and lower limits are not higher than half of the amplitude of the phase current. For the isolated bus half-controlled system or the common bus half-controlled system with high power factor, the upper and lower limits can be 0.1 to 0.2 times of the amplitude of the phase current.

[0055] ​After the current of a certain phase enters the current zero-crossing region of the corresponding phase, the small-power fully-controlled switch of the corresponding phase in the second converter can act, while the small-power fully-controlled switches of the other two phases cannot act. That is, after the current of a certain phase enters the current zero-crossing region, the small-power fully-controlled switch of the phase in the second converter can act, that is, the switch state of the phase bridge arm can be freely controlled, while the switch states of the bridge arms of the other two phases in the second converter are determined only by the switch states of the diodes, that is, controlled by the current direction. In this case, the voltage vector output by the second converter will be synthesized by the adjacent two active voltage vectors. Since there is no participation of zero vectors, the voltage vector output by the second converter only falls on the boundary line of the modulation region in the current zero-crossing region.

[0056] To ensure that the reference voltage vector of the second converter does not exceed its modulatable range and reduce the calculation complexity, its direction is oriented to the current vector, so the amplitude of the voltage vector output by the second converter is as follows:

[0057] ;

[0058] ;

[0059] ;

[0060] ;

[0061] In the formula, I is the current vector, and φ is the included angle between the axis of the current vector and the axis of the voltage vector. θ i The current vector is I. i s The included angle between the axis of the current vector and the axis of the voltage vector is φ. α mod represents the remainder function, that is, θ v2 The included angle is φ. θ i Divided by the remainder of π / 3.

[0062] According to the directional relationship between the output voltage vector V ref2 and the current vector, the output voltage vector V ref2 of the second converter is calculated. α The axis reference voltage of the second converter is V. u α2 * The axis reference voltage of the second converter is V. β u β2 * The formula is as follows:

[0063] ;

[0064] The reference voltage in the dq coordinate system is transformed by coordinate transformation​u q2 * and u d2 * Convert to αβ Under the coordinate system, we get α axis reference voltage u α2 * and β axis reference voltage u β2 * Since the small power controlled switch on the corresponding phase bridge arm of the second converter in the current zero-crossing region can act at this time, and the small power controlled switches of the other two phases cannot act, the output high level or low level is determined by the conduction and turn-off of the current control diode, so the modulation wave driving the corresponding phase of the second converter can be obtained through the space vector modulation based on the adjacent two vectors, that is, the corresponding phase small power controlled switch is controlled by the control signal. At this time, the small power controlled switches of the remaining phases in the second converter are in the off state.

[0065] At this time, the first converter is in αβ Under the coordinate system, we get α axis reference voltage u α1 * and β axis reference voltage u β1 * The calculation method of changes, the formula is as follows:

[0066] ;

[0067] .

[0068] Subsequently, through space vector modulation, the modulation wave driving the first converter can be output, that is, all the controlled switches of the first converter are controlled by the control signal to realize the modulation of the first converter.

[0069] In addition, for the half-controlled winding permanent magnet synchronous generator system with common bus feeding as shown in Figure 7 , the same strategy can also improve the zero sequence compensation capability of the system, Figure 8 is a schematic diagram of the modulable range of the first converter when the system adopts a typical control method in the current zero-crossing region of the B-phase current; Figure 9Fig. 1 is a schematic diagram of the modulatable range of the first converter when the system adopts the improved control method in the current zero-crossing region of the B-phase current, wherein the orange region represents that the first converter can achieve full compensation of the zero-sequence vector generated when the first converter and the second converter output voltage vectors, and the gray region represents that the voltage vector synthesized by the first converter and the second converter must contain a positive or negative zero-sequence component; by comparing Figure 8 and Figure 9 It can be seen that, by using the control method provided in the present application, the zero-sequence compensation capability of the improved semi-controlled open-winding permanent magnet synchronous generator system is improved.

[0070] In summary, compared with the prior art, the technical solution provided in the present application introduces a small-power fully-controlled switch to make the output voltage vector of the second converter no longer determined by the current direction, which can weaken the adverse effects caused by current sampling errors and delays, and improve the zero-sequence compensation capability of the semi-controlled open-winding permanent magnet synchronous generator system. Furthermore, the excessively long current zero-crossing duration caused by the uncontrollable output voltage of the diode rectifier in the prior art can be completely eliminated, and the suppression of harmonic currents can be achieved; the small-power fully-controlled switch in the second converter can effectively reduce the cost; by setting a suitable current zero-crossing region, stable switching of different control methods can be achieved, and the fully-controlled switch device in the second converter only needs to flow a low current.

Claims

1. A semi-controlled open-winding permanent magnet synchronous generator system, characterized in that: It includes a first converter, an open-winding permanent magnet synchronous generator and a second converter; The AC ends of the first converter and the second converter are respectively connected to two sides of the stator winding of the open-winding permanent magnet synchronous generator; The first converter includes three-phase bridge arms, each phase bridge arm includes two fully controlled switches with freewheeling diodes connected in series; The second converter includes three-phase bridge arms, each of which includes two diodes connected in series; each diode is anti-parallel-connected to a low-power fully-controlled switch without a freewheeling diode; in, V 1= V 2= V 3； I 1= I 2≥5 I 3； Where, V 1. V 2 and V 3 are the rated voltages of the fully controlled switch, diode and low-power fully controlled switch respectively; I 1. I 2 and I 3 are the rated currents of the fully controlled switch, diode and low-power fully controlled switch respectively; in, Outside the current zero-crossing region, all low-power fully-controlled switches in the second converter are in the off state; When the current of a certain phase enters the corresponding current zero-crossing region, the low-power full-controlled switch of the corresponding phase in the second converter is actuated, and the low-power full-controlled switches of the other two phases are inactive.

2. A control method for a semi-controlled open-winding permanent magnet synchronous generator system according to claim 1, characterized in that: Including the control method in the current zero-crossing area, as follows: A. A control method for a first converter, comprising the following steps: Step S1: Collect the three-phase current of the semi-controlled open-winding permanent magnet synchronous generator system i a 、 i b 、 i c Then, based on the rotor electrical angle θ e Obtained by coordinate transformation dq Under the coordinates d Shaft current i d and q-axis current i q ; Step S2: Calculation d Shaft current i d and d Axis reference current i d * The difference Δ i d , q Shaft current i q and q Axis reference current i q * The difference Δ i q ;in, i d * =0; The difference Δ i d Sum difference Δ i q Perform PI control processing respectively and get d Axis reference voltage u d * and q Axis reference voltage u q * ; Step S3: Based on the rotor electrical angle θ e Respectively d Axis reference voltage u d * and q Axis reference voltage u q * Convert to αβ Coordinate system, get α Axis reference voltage u α * and β Axis reference voltage u β * ; Step S4: Calculation α Axis reference voltage u α * With reference voltage u α2 * The sum of the first converter is obtained α Axis reference voltage u α1 * ;calculate β Axis reference voltage u β * With reference voltage u β2 * The sum of the first converter is obtained β Axis reference voltage u β1 * ; Among them, the reference voltage u α2 * and reference voltage u β2 * are the output voltage vectors of the second converter in the current zero crossing region. V ref2 of α Axis reference voltage and β Axis reference voltage; Step S5: α Axis reference voltage u α1 * and β Axis reference voltage u β1 * Performing space vector modulation to obtain a first control signal to control the fully controlled switch in the first converter; B. A control method for the second converter, comprising: Set the reference voltage u α2 * and reference voltage u β2 * Perform space vector modulation to obtain a second control signal to control two low-power fully-controlled switches of corresponding phases in the second converter; meanwhile, the low-power fully-controlled switches of other phases are in the off state.

3. The control method of a semi-controlled open-winding permanent magnet synchronous generator system according to claim 2, characterized in that: Also includes calculation of reference voltage u α2 * and reference voltage u β2 * , the formula is as follows: ； Based on the rotor electrical angle θ e Respectively d Axis reference voltage u d2 * and q Axis reference voltage u q2 * Convert to αβ Coordinate system, get the reference voltage u α2 * and reference voltage u β2 * .

4. The control method of a semi-controlled open-winding permanent magnet synchronous generator system according to claim 2, characterized in that: It also includes a control method outside the current zero-crossing region, and the specific steps are as follows: Step Q1: Calculation α Axis reference voltage u α * With voltage u α2 and, replace the first converter α Axis reference voltage u α1 * ; calculate β Axis reference voltage u β * With voltage u β2 and, replace the first converter β Axis reference voltage u β1 * ; Among them, voltage u α2 and voltage u β2 are the output voltage vectors of the second converter outside the current zero-crossing region. V ref2 of α Axis components and β Axis component; Step Q2: Replace the α Axis reference voltage u α1 * and β Axis reference voltage u β1 * Performing space vector modulation to obtain a third control signal to control all fully controlled switches in the first converter; At the same time, all low-power fully-controlled switches in the second converter are in the off state.

5. The control method of a semi-controlled open-winding permanent magnet synchronous generator system according to any one of claims 2 to 4, characterized in that: The upper and lower boundaries of the zero-crossing region are both provided with hysteresis loops; At the preset ratio, an upper boundary hysteresis loop is drawn on both sides of the upper boundary of the zero-crossing region. I L- , I L+ ], a lower boundary hysteresis loop is drawn on both sides of the lower boundary of the zero-crossing region [- I L+ ,- I L- ]; For any phase current, The first time it is greater than the upper limit of the lower boundary hysteresis loop - I L- , indicating that it enters the zero-crossing region until it exceeds the upper limit of the upper boundary hysteresis loop I L+ Or less than the lower limit of the lower hysteresis band - I L+ , indicating leaving the zero-crossing area; or, The first time it is less than the lower limit of the upper hysteresis band I L- , indicating that it enters the zero-crossing region until it exceeds the upper limit of the upper boundary hysteresis loop I L+ Or less than the lower limit of the lower hysteresis band - I L+ , indicating leaving the zero-crossing region.

6. The control method of a semi-controlled open-winding permanent magnet synchronous generator system according to any one of claims 2 to 4, characterized in that: Also includes calculating the output voltage vector of the second converter in the current zero crossing area V ref2 , the formula is as follows: ； ； ； Where, U dc2 is the DC bus voltage amplitude of the second converter, θ i is the current vector i s and α The angle of the axis, θ v2 Angle θ i The remainder after dividing by π / 3.

Images