CN105846699B - A kind of three-phase controlled rectifier model predictive control method based on switch list - Google Patents
A kind of three-phase controlled rectifier model predictive control method based on switch list Download PDFInfo
- Publication number
- CN105846699B CN105846699B CN201610185735.5A CN201610185735A CN105846699B CN 105846699 B CN105846699 B CN 105846699B CN 201610185735 A CN201610185735 A CN 201610185735A CN 105846699 B CN105846699 B CN 105846699B
- Authority
- CN
- China
- Prior art keywords
- vector
- voltage
- active
- reactive power
- switch list
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Active
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration
Abstract
The invention discloses a kind of three-phase controlled rectifier model predictive control method based on switch list, includes the following steps：(1) network voltage vector angle is divided into 12 sectors, vector is controlled using eight candidate voltages to three-phase controlled rectifier；(2) grid side of foundation three-phase controlled rectifier is active and reactive power is with the changing rule of network voltage vector angle, determines the corresponding candidate voltage control vector in each sector, generates switch list；(3) the current affiliated sector of network voltage vector angle is judged at current time, and corresponding candidate voltage control vector is extracted from switch list；(4) according to the candidate voltage vector prediction subsequent time of extraction grid side is active and reactive power, therefrom choose optimum voltage and control vector.Switch list and Model Predictive Control Algorithm are combined by the present invention, are excluded most of voltage vector to be selected by switch list, are significantly reduced calculation amount.
Description
Technical field
The invention belongs to rectifier control technology fields, more particularly, to a kind of model prediction control based on switch list
Method processed.
Background technology
Three-phase controlled rectifier can preferable stable DC busbar voltage, load change when, DC bus electricity
Pressure energy is enough stablized near reference value, simultaneously, additionally it is possible to control the power factor (PF) of net side, realize that power factor is 1 operation, and produce
Raw current harmonic content is smaller.Therefore, in recent years, in order to improve the working efficiency and performance of rectifier, controlled rectification
Constantly replace uncontrollable rectifier.
Three-phase controlled rectifier is since switching device can arbitrarily be opened and turn off, the spirit that working method compares
It is living, by being combined with different control strategies, it can realize different working performances.The current main control strategies of rectifier are divided into
Voltage oriented control and direct Power Control.Voltage oriented control is divided into active point by carrying out decoupling to electric current dq axis components
Amount and reactive component, this control method are similar with the vector control method of motor.But between dq shaft currents, there are couplings
It closes, is not completely to decouple, and the complexity that the parameter tuning of current inner loop can compare.Therefore, voltage oriented in order to make up
Deficiency, direct Power Control replaced the current inner loop of voltage oriented control by switch list, eliminates complicated coordinate transform,
Also directly the active and reactive power of rectifier is controlled there is no intercoupling between dq shaft currents simultaneously, is rung
Answer speed faster than voltage oriented.But due to only acting on the switch of a voltage vector and rectifier in a switch periods
Table be in advance it is selected can not change with the working condition of rectifier, therefore direct Power Control generate power
Fluctuation can compare big.
With the fast development of microprocessor, the promotion of processor computing capability so that some advance control algorithms can
It applies in rectifier.Wherein Model Predictive Control has obtained grinding extensively for Most scholars with its preferable control performance
Study carefully.Therefore, in order to make up the deficiency of above-mentioned direct Power Control, Model Predictive Control and direct Power Control are combined to obtain
The power prediction of rectifier controls, and this control algolithm by being calculated rectifier optimal voltage vector online so that in office
The voltage vector that the meaning moment is selected all is optimal, and control performance can pass through fixed switch list selection electricity than direct Power Control
The effect that pressure vector obtains wants better.But it is big due to comparing in the calculation amount of line computation, therefore, it is necessary to better performances
Processor can realize power prediction control algolithm.
Invention content
For the disadvantages described above or Improvement requirement of the prior art, the present invention provides a kind of model predictions based on switch list
Voltage to be selected is controlled vector by switch list and excludes a part, to reduce due to selecting optimum voltage control by control method
It is computed repeatedly caused by vector processed, since switch list is the voltage vector to be selected for excluding some suboptimums, optimal voltage control arrow
Amount still gives Model Predictive Control Algorithm to select, therefore while reducing calculation amount, remains able to the electricity for ensureing selection
Voltage-controlled vector processed is optimal at any time.
To achieve the above object, a kind of three-phase controlled rectifier model predictive control method based on switch list, including such as
Lower step：
(1) network voltage vector angle is divided into 12 sectors, to three-phase controlled rectifier using eight candidate voltages
Control vector；
(2) according to three-phase controlled rectifier grid side is active and reactive power with network voltage vector angle variation
Rule determines the corresponding candidate voltage control arrow in each sector in conjunction with the comparison result of active and reactive power and reference value
Amount generates switch list；
(3) at current time, judge the current affiliated sector of network voltage vector angle, and according to current active and
Reactive power and reference value comparison result extract corresponding candidate voltage control vector from switch list；
(4) according to the candidate voltage vector prediction subsequent time of extraction grid side is active and reactive power, Cong Zhongxuan
It takes closest to grid side is active and the corresponding candidate voltage control vector of reactive power reference qref is as optimum voltage control arrow
Amount.
Further, the grid side of the three-phase controlled rectifier is active and reactive power is with network voltage vector angle
Changing rule be expressed as：
Wherein, dp is the change rate of grid side active power, and dq is the change rate of grid side reactive power；θ closes for power grid
At vector angle, candidate voltage control vector ViIn the component of α axisCandidate voltage control vector ViIn point of β axis
AmountVoltage vector modulus valueVdcFor DC bus-bar voltage.
Further, the switch list is as shown in the table：
In table, θ1,θ2,…θ11,θ12Network voltage vector angle is indicated successively
12 sectors
Further, the step (4) according to the candidate voltage vector prediction subsequent time of extraction grid side it is active with
And the specific implementation of reactive power is：
Wherein：The active-power P at current timekAnd reactive power QkIt is expressed asVαkWith
VβkFor current electric grid voltage vector α beta -axis components；ViαkAnd ViβkFor current time voltage control vector α, β axis component；LsFor
Net side inductance；ω is the angular frequency of power grid；RsFor net side resistance；TsFor the sampling period.
In general, through the invention it is contemplated above technical scheme is compared with the prior art, have below beneficial to effect
Fruit：
1, it is opened in line computation selection optimum voltage control vector since switch list used by Direct Power is fixed
It is impossible to meet rectifiers under arbitrary working condition is all optimal for voltage vector in the table of pass, therefore Model Predictive Control is calculated
The voltage control vector that method is selected is more accurate compared with direct Power Control method, and obtained control performance also can be more excellent.
2, Model Predictive Control Algorithm and switch list are combined, exclude some voltage controls to be selected in advance by switch list
Vector, while it is optimal to ensure the voltage selected control vector so that the number of voltage control vector to be selected reduces, from
And reduce the calculation amount of Model Predictive Control Algorithm.
Description of the drawings
Fig. 1 is the schematic diagram of rectifier；
Fig. 2 is rectifier active power variation diagram；
Fig. 3 is rectifier reactive power variation diagram；
Fig. 4 is control method flow chart of the present invention；
Fig. 5 is the Model Predictive Control block diagram the present invention is based on switch list.
Specific implementation mode
In order to make the purpose , technical scheme and advantage of the present invention be clearer, with reference to the accompanying drawings and embodiments, right
The present invention is further elaborated.It should be appreciated that the specific embodiments described herein are merely illustrative of the present invention, and
It is not used in the restriction present invention.As long as in addition, technical characteristic involved in the various embodiments of the present invention described below
It does not constitute a conflict with each other and can be combined with each other.
Main technical points are described in detail first：
A, voltage control vector V to be selectedi
Network voltage vector angle is divided into 12 sectors by the present invention, to three-phase controlled rectifier using eight candidate electricity
Voltage-controlled vector processed.Since rectifier has 8 kinds of on off states, corresponding 8 kinds different voltage to be selected control vector ViValue such as following table
It is shown：
Wherein, ViExpression voltage control vector, i=0 ..., 7,For the on off state of rectifier three-phase bridge arm, ViαWith
ViβV is indicated respectivelyiIn the component of α axis and β axis, VdcFor DC bus-bar voltage.
B, prediction subsequent time grid side is active and reactive power
Mathematical model under three phase coordinate system of rectifier is as follows：
Wherein： For the on off state of rectifier three-phase bridge arm；For grid side three-phase electricity
Pressure；For grid side three-phase current；VdcFor DC bus-bar voltage；LsFor net side inductance；RsFor net side resistance；vnNFor in net side
Voltage between property point and DC bus negative polarity point is as shown in Figure 1.
Since rectifier grid side is balanced three-phase voltage source, can obtain：
Simultaneous formula (1) and formula (2) can obtain：
It enables：
Wherein：Formula (1) can be expressed in the form of space vector by formula (4)：
In order to which space vector to be transformed under α β coordinate systems, enable：
The expression formula of instantaneous power is：
Simultaneous formula (6) and formula (7) can obtain expression formula of the instantaneous power under α β coordinate systems：
In order to predict that rectifier is active and idle, carrying out derivation to formula (8) can obtain：
Due to there is the variable quantity of voltage and current in formula (9), and this tittle is difficult to directly measure, it is therefore necessary to find out
The variable quantity of voltage and current under α β coordinate systems, and the change rate that electric current can be obtained by formula (5) is：
It is assumed that voltage on line side amplitude and frequency-invariant, power grid resultant vector will be revolved with constant amplitude and angular speed in space
Turn, then the grid voltage change rate under α β coordinate systems there will be following relationship：
Wherein：ω is the angular frequency of power grid.
Formula (10) and (11) are brought into can obtain in formula (9) active without containing voltage and current variable quantity and
The expression formula of idle change rate：
Formula (12) progress discretization can acquire to rectifier is active and the expression formula of reactive power prediction is：
Wherein：TsFor the sampling period.
According to upper table it is found that ViαAnd ViβOne shares 8 kinds of different values.This 8 kinds of different values are brought into formula
(13) the active and reactive power of prediction subsequent time in.
C, switch list is generated
It is assumed that network voltage resultant vector VsIt is remained unchanged within a very short sampling period.So formula (9) can letter
It turns to：
Formula (10) is brought into formula (15), then the change rate that can obtain active P and idle Q is as follows：
Wherein：Dp is the change rate of grid side active power, and dq is the change rate of grid side reactive power；θ closes for power grid
At vector angle, candidate voltage control vector ViIn the component of α axisCandidate voltage control vector ViIn point of β axis
AmountVoltage vector modulus valueVdcFor DC bus-bar voltage.
The voltage vector and net side synthesized with rectifier according to the active and idle change rate of formula (16) rectifier
Voltage-phase is related.More accurate switch list is obtained for the ease of analysis, formula (16) is graphically showed, such as
Shown in Fig. 2 and 3.
X-axis in Fig. 2 and 3 represents the angle of power grid resultant vector and α axis, and y-axis represents active and idle variation
Value, vector Vi(i=0,1 ... 7) represents 8 kinds of differences voltage control vector to be selected that rectifier can be generated, θi(i=1,2 ... 12)
Represent 12 different sectors according to power grid resultant vector and the angular divisions of α axis.
It is assumed that SpFor the sluggish comparison result of active power, SqFor reactive power sluggishness comparison result.In order to make DC bus
Voltage stabilization is near reference value, while it is always 1 to maintain the power factor (PF) of power grid.It just has to so that active power tracking ginseng
Value is examined, reactive power is maintained 0.Therefore, active to be less than given value and nothing when network voltage resultant vector is in the 1st sector
When work(is less than zero, SpAnd SqValue is 1.In order to allow active increase, should choose be more than in the sectors Fig. 210 voltage vector：V4,V5,
V6,V3,V0,V7；Simultaneously in order to allow idle increase, should choose be more than in the sectors Fig. 310 voltage vector：V3,V2,V4,V0,
V7.So, enabling to active and idle increased vector should be：V3,V4,V0,V7.Therefore, it opens in this case
Vector in the table of pass should be：V3,V4,V0,V7.Rectifier all working situation is taken into account, switch list can be obtained such as
Shown in lower.
D, object function
Control vector to select best voltage, from candidate voltage control vector choose closest to grid side it is active with
And the corresponding candidate voltage control vector of reactive power reference qref controls vector as optimum voltage.
When practical application, an object function can be constructed to be selected so that the voltage to be selected of target function value minimum
It is that optimum voltage controls vector to control vector.As an example, the object function that the present invention constructs is as follows：
G=(P*-Pk+1)2+(Q*-Qk+1)2 (14)
Wherein：P*And Q*For active and idle reference value, Pk+1And Qk+1For active and idle predicted value.
Fig. 4 is referred to, a kind of model predictive control method based on switch list of the present invention specifically includes following steps：(1)
Network voltage vector angle is divided into 12 sectors, vector is controlled using eight candidate voltages to three-phase controlled rectifier；
(2) according to three-phase controlled rectifier grid side is active and reactive power with network voltage vector angle variation
Rule determines the corresponding candidate voltage control arrow in each sector in conjunction with the comparison result of active and reactive power and reference value
Amount generates switch list；
(3) at current time, judge the current affiliated sector of network voltage vector angle, and according to current active and
Reactive power and reference value comparison result extract corresponding candidate voltage control vector from switch list；
(4) according to the candidate voltage vector prediction subsequent time of extraction grid side is active and reactive power, Cong Zhongxuan
It takes closest to grid side is active and the corresponding candidate voltage control vector of reactive power reference qref is as optimum voltage control arrow
Amount.
Model Predictive Control block diagram based on switch list is as shown in Figure 5.It is compared with Model Predictive Control, after the present invention improves
Algorithm voltage to be selected reduced by switch list control vector number, being reduced to most 4 voltages by original 8 voltage vectors swears
Amount, reduces the amount of computing repeatedly of more than half.Improved control strategy is in the nature Model Predictive Control, selects optimum voltage
Control vector process with it is noted earlier similar, some voltages to be selected control vectors are only excluded by switch list.Due to opening
Pass table can only exclude the voltage vector of suboptimum, can't optimal voltage be controlled vector and excluded, thereby it is ensured that selected
Voltage vector be optimal voltage control vector.In short, improved algorithm can subtract under the premise of not influencing algorithm performance
The calculation amount of mini Mod predictive control algorithm.
As it will be easily appreciated by one skilled in the art that the foregoing is merely illustrative of the preferred embodiments of the present invention, not to
The limitation present invention, all within the spirits and principles of the present invention made by all any modification, equivalent and improvement etc., should all include
Within protection scope of the present invention.
Claims (3)
1. a kind of three-phase controlled rectifier model predictive control method based on switch list, which is characterized in that include the following steps：
(1) network voltage vector angle is divided into 12 sectors, to three-phase controlled rectifier using eight candidate voltage controls
Vector；
(2) grid side of foundation three-phase controlled rectifier is active and reactive power is advised with the variation of network voltage vector angle
Rule determines the corresponding candidate voltage control vector in each sector in conjunction with the comparison result of active and reactive power and reference value,
Generate switch list；
(3) at current time, judge the current affiliated sector of network voltage vector angle, and according to current active and idle
Power and reference value comparison result extract corresponding candidate voltage control vector from switch list；
(4) according to the candidate voltage vector prediction subsequent time of extraction grid side is active and reactive power, therefrom choose most
Close to grid side is active and the corresponding candidate voltage control vector of reactive power reference qref is as optimum voltage control vector；
The grid side of the three-phase controlled rectifier is active and reactive power with network voltage vector angle changing rule table
It is shown as：
Wherein, dp is the change rate of grid side active power, and dq is the change rate of grid side reactive power；θ is power grid synthesis arrow
Measuring angle, candidate voltage control vector ViIn the component mark pressure value of α axisCandidate voltage control vector ViIn β axis
Component mark pressure valueI=0 ..., 7, voltage vector modulus valueVdcFor DC bus-bar voltage, ViαWith
ViβCandidate voltage control vector V is indicated respectivelyiIn the component of α axis and β axis, VsFor network voltage resultant vector.
2. three-phase controlled rectifier model predictive control method according to claim 1, which is characterized in that the switch list
As shown in the table：
In table, θ1,θ2,…θ11,θ12Network voltage vector angle is indicated successively
12 sectors
3. three-phase controlled rectifier model predictive control method according to claim 1 or 2, which is characterized in that the step
Suddenly (4) according to extraction candidate voltage vector prediction subsequent time grid side is active and the specific implementation of reactive power
For：
Wherein：The active-power P at current timekAnd reactive power QkIt is expressed asVαkAnd VβkFor
Current electric grid voltage vector α, beta -axis component, IαkAnd IβkFor current electric grid current phasor α, beta -axis component；ViαkAnd ViβkWhen being current
Carve voltage control vector α, β axis component；LsFor net side inductance；ω is the angular frequency of power grid；RsFor net side resistance；TsTo adopt
The sample period.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201610185735.5A CN105846699B (en) | 2016-03-29 | 2016-03-29 | A kind of three-phase controlled rectifier model predictive control method based on switch list |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201610185735.5A CN105846699B (en) | 2016-03-29 | 2016-03-29 | A kind of three-phase controlled rectifier model predictive control method based on switch list |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CN105846699A CN105846699A (en) | 2016-08-10 |
| CN105846699B true CN105846699B (en) | 2018-07-24 |
Family
ID=56584044
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CN201610185735.5A Active CN105846699B (en) | 2016-03-29 | 2016-03-29 | A kind of three-phase controlled rectifier model predictive control method based on switch list |
Country Status (1)
| Country | Link |
|---|---|
| CN (1) | CN105846699B (en) |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102931857A (en) * | 2012-10-26 | 2013-02-13 | 河南师范大学 | Predictive control method of voltage-type PWM (pulse-width modulation) rectifier fixed-frequency model |
| CN103427738A (en) * | 2013-08-25 | 2013-12-04 | 浙江大学 | Optimal predictive direct power control method of doubly fed induction generator |
| CN104022662A (en) * | 2014-06-27 | 2014-09-03 | 北方工业大学 | PWM (Pulse-Width Modulation) rectifier control method and PWM rectifier control device based on model prediction control |
| CN104617798A (en) * | 2015-03-05 | 2015-05-13 | 河南师范大学 | Vector number-variable direct power control method for three-phase power converter |
-
2016
- 2016-03-29 CN CN201610185735.5A patent/CN105846699B/en active Active
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102931857A (en) * | 2012-10-26 | 2013-02-13 | 河南师范大学 | Predictive control method of voltage-type PWM (pulse-width modulation) rectifier fixed-frequency model |
| CN103427738A (en) * | 2013-08-25 | 2013-12-04 | 浙江大学 | Optimal predictive direct power control method of doubly fed induction generator |
| CN104022662A (en) * | 2014-06-27 | 2014-09-03 | 北方工业大学 | PWM (Pulse-Width Modulation) rectifier control method and PWM rectifier control device based on model prediction control |
| CN104617798A (en) * | 2015-03-05 | 2015-05-13 | 河南师范大学 | Vector number-variable direct power control method for three-phase power converter |
Non-Patent Citations (2)
| Title |
|---|
| "Elimination of Power Control Coupling in Direct Power Control Based on Switching Table for Three-level PWM Rectifier";Ting Lu 等;《Electrical Machines and Systems (ICEMS), 2010 International Conference on》;20101210;全文 * |
| "Multiple switching tables direct power control of active front-end rectifiers";Joaquín G. Norniella 等;《IET Power Electronics 》;20140619;第7卷(第6期);第1578-1589段 * |
Also Published As
| Publication number | Publication date |
|---|---|
| CN105846699A (en) | 2016-08-10 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN106788027B (en) | A kind of model predictive control method and system based on optimal two vectorial combination | |
| Qasim et al. | Optimal current harmonic extractor based on unified ADALINEs for shunt active power filters | |
| Liu et al. | Overview of advanced control strategies for electric machines | |
| CN103956919A (en) | Simplified model forecasting control method of network voltage unbalance three-level rectifier | |
| Yu et al. | Model-free predictive current control for three-level inverter-fed IPMSM with an improved current difference updating technique | |
| Mossa et al. | Cost-effective predictive flux control for a sensorless doubly fed induction generator | |
| CN110034690A (en) | A kind of Vienna rectifier model prediction Virtual shipyard control method | |
| CN109728756B (en) | Double-reference-voltage single-vector open winding permanent magnet motor prediction control method and equipment | |
| CN110445438A (en) | A kind of permanent magnet synchronous motor prediction flux linkage control method based on extension domination set | |
| Mimouni et al. | Vectorial command of an asynchronous motor fed by a photovoltaic generator | |
| CN105762789B (en) | A kind of 3-phase power converter model predictive control method of Converter Without Voltage Sensor | |
| Emanuel et al. | Clarke's alpha, beta, and zero components: a possible approach for the conceptual design of instrumentation compatible with IEEE Std. 1459–2000 | |
| Al Azze et al. | Reducing torque ripple of induction motor control via direct torque control | |
| CN105846699B (en) | A kind of three-phase controlled rectifier model predictive control method based on switch list | |
| CN109802615A (en) | Double vector winding open circuit permanent magnet synchronous motor current predictive control methods and equipment | |
| Dieng et al. | Fault-tolerant control of 5-phase pmsg for marine current turbine applications based on fractional controller | |
| CN112467776B (en) | Current source type converter system, control method and space vector modulation method | |
| Li et al. | Mitigation of voltage sag for DVR to comply with voltage security protocol via elliptical trajectory compensation | |
| CN107276123A (en) | A kind of variable coefficient frequency reducing model prediction direct Power Control method and device | |
| Roy et al. | A photovoltaic-based improved excitation control strategy of three-phase self-excited induction generator suitable for wind power generation | |
| Cortes-Vega et al. | Optimal tracking control for a Permanent Magnet Synchronous Generator | |
| Rasouli et al. | An efficient approach for measurement-based composite load modeling | |
| Kim et al. | Inverter average input power estimation algorithm in low-frequency modulation index operation of permanent magnet synchronous motors | |
| Chen et al. | Control and performance analysis for a capacitor-coordinated static synchronous compensator to enhance dynamic compensation capability | |
| Bhuvaneshvari et al. | PI and fuzzy based sensor less speed control of induction motor |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| C06 | Publication | ||
| PB01 | Publication | ||
| C10 | Entry into substantive examination | ||
| SE01 | Entry into force of request for substantive examination | ||
| GR01 | Patent grant | ||
| GR01 | Patent grant |