外文翻译--公共接地无刷直流电机驱动系统的FPGA实现.docx

附录ACommon-grounded BLDCM Drive System Based on FPGAPinghua Tang, Tiecai Li Department of Electrical Engneering Harbin Industry of Technology harbin, CHINA Email: ; Abstract This paper proposed a kind of common-grounded brushless DC motor(BLDCM)drive system based on field programmed gate array(FPGA)control. The proposed system has two characteristics: one is that the former 60 of every drive lag applies pulse width modulation (PWM) and the latter 60 conducts constantly (PWM_ON modulation); the other is that there are no isolating optical couplers between control circuit and drive circuit. So the proposed system has some advantages such as reducing ripple of electromagnetic torque, simplifying drive circuit to reduce the delay of signals, and reducing the cost and bulk of drive system. A prototype is designed based on FPGA chip, and experimental results demonstrated the validity of relative theory.Index Terms - common-grounded drive; BLDCM; FPGA; PWM_ON modulationI. INTRODUCTIONBrushless DC motor is widely applied in modern control system because of many advantages such as high efficiency, high power density, good speed characteristic and simplified control etc.1-2. In order to control BLDCM system effectively, conventional drive scheme for BLDCM system is that 120 control signals which is output by control circuit are isolated by optical couplers, then deliver to drive circuit and control the power main circuit. So conventional BLDCM system presents some disadvantages such as big electromagnetic torque ripples, big volume, high cost, and signals delay by optical coupler etc. These disadvantages make conventional BLDCM system not been used in some conditions which need high precision and high stability 3-4. To overcome these disadvantages of conventional BLDCM system to some extent, this paper presents a novel BLDCM system which is applied with PWM_ON modulation and common-grounded drive scheme. The proposed system has two characteristics: one is PWM_ON modulation control mode that the former 60 of every drive lag applies pulse width modulation (PWM) and the latter 60 conducted constantly in 120 period; the other is that there are no isolating optical couplers between control circuit and drive circuit. This paper deduced mathematics model of BLDCM, then analyzed operational principle of the PWM_ON modulation common-grounded drive scheme which is used to BLDCM system, and simulation analysis about the proposed scheme is presented, finally, a 120W BLDCM system prototype is developed based on FPGA chip, and experimental results were analyzed.II. BLDCM MATHEMATICAL MODEL Most BLDCM drives are based on the active control to three-phase inverter to obtain square-wave current of BLDCM needed in modern times. The BLDCM mathematical model which infers below in this article includes three-phase inverter. The mathematical model of BLDCM is composed of two parts, namely mechanical equation and voltage equation. This paper makes the following three suppositions before introducing the mathematical model, as follows: (1) Three-phase stator winding A, B, C is symmetrical in spatial distribution, the higher harmonic component of magnetic field is neglected. (2) The magnetic saturation and the core loss (magnetic hysteresis loss, eddy current loss) are neglected. (3)The influence factors including temperature, frequency etc. on parameters of motor are not considered. Mechanical movement equation of electric machine is fixed and wont change with the coordinate transformation. BLDCM mechanical movement equation is as follows:Te Tl =J + B (1)where Te is electromagnetic torque, TL is load torque, J is rotor and load inertia, B is friction coefficient,is rotating speed of BLDCM. Take the three-phase stator voltage as the state variable. Its voltage balance equation can be expressed as (2):Ua Ra ia La Lab Lac ia eaUb = Rb ib + Lba Lb Lbc ib + eb (2)Uc Rc ic Lca Lcb Lc ic ec Because the rotor is permanent-magnet ,La ,Lb ,Lc ,Lab ,Lba ,Lac ,Lca ,Lbc ,Lcb , can be considered as constants, then,Ra=Rb=Rc=RsLa=Lb=Lc=LLab=Lba=Lac=Lca=Lbc=Lcb=M (3)ia+ib+ic=0Therefore, we obtain the PM BLDCM voltage equation which is shown in (4):Ua Rs ia LM ia ea Ub = Rs ib + LM ib + eb (4)Uc Rs ic LM ic ecThe topology of BLDCM model is obtained from (4) and shown in Fig.1.Fig.1 Topology of BLDCM modelSo, mathematical model of BLDCM can be described as (1) and (4).III. PWM_ON MODULATIONCOMMON-GROUNDED DRIVE SCHEMEAs three-phase inverter is concerned, PWM control scheme is widely applied to control the speed and current of BLDCM control system. There are following common-used PWM modulation modes: H_PWM&L_ON, H_ON&L_PWM and H_PWM&L_PWM. The first two kinds of modes can be realized simply but has the disadvantage of big phase current pulsation in every electric cycle. The last one is studied a lot for its advantage of reducing current pulsation, but switching loss is too big.However, the control systems which apply the modulations above, the control part is isolated with the drive part. That is to say, there are optical couplers between control circuit and drive circuit. The optical couplers must cause signals delay to worse characteristic of system. On the other hand, this method will affect reliability of the driver and enhance the cost. PWM_ON modulation and common ground control scheme will be introduced.A. PWM_ ON modulationThe circuit topology of BLDCM is showed in Figure 1. The traditional control scheme is using three-phase six conditions and 120 degree conduction mode. To produce a constant electromagnetic torque, it is required to feed rectangular currents in the flat position of the ideal trapezoidal back EMF. However, the commutation of phase-currents requires a finite time due to the inductance of machine windings, and torque pulsation may occur accordingly. Some research discovered that torque pulsation size is related with the non inverting commutation current and changes with the modulation modes.At present, the main kinds of PWM modulations are: the switches in the upper-half lag modulated and in the lower-half lag 120 degree on(H_PWM), the switches in the lower-half lag modulated and in the upper-half lag 120 degree on(L_PWM), switches of both the upper lag and the lower lag modulated(H_PWM-L_PWM), the first 60 degree PWM and latter 60 degree on in the both upper and lower switches(PWM_ON), the first 60 degree on and latter 60 degree PWM in the both upper and lower switches and so on. The research shows that PWM_ON modulation has the advantage of the smallest torque ripple and switches loss. The timing diagram is shown in Fig 2.Fig.2 Timing diagram of PWM_ON control signalsThe electromagnetic torque of electrical machine can be expressed with (5):Te =(eaia+ebib+ecic) (5)Where, Te represents electromagnetic torque, p is pole pairs, represents electrical rotating speed, ea ,eb and ec represent phase back electromotive force, ia, ib and ic represent phase current.When electrical machine operates conventional control scheme and neglects influence of phase conversion, the electromagnetic torque of electrical machine can be expressed as (6):Te=2pkei (6)Where, ke represents electromagnetic time coefficient, i is current of steady state.In order to describe the torque ripple of phase conversion causing by PWM_ON modulation, this paper will take period 60, 120 for example to deduce it.Three phase currents showed in(7)can be obtained according the mathematical model of BLDCM.ia(t)=i-(2ke+2Rsi+DU)tib(t)= （DU-ke）t (7)ic(t)=-i+(4ke+3Rsi+DU)tWhere, U is bus voltage, D is duty cycle of PWM.According to (5) and (7), the electromagnetic torque of BLDCM system with PWM_ON modulation can be described by (8):Te=2pkei +2UDt-8ket-6Rsit (8)The ripple of electromagnetic torque can be expressed as:TeT=8ket+6Rsit -2UDt (9)From (9), it is definite that the ripple of electromagnetic torque is determined by and D. So the minimal ripple of electromagnetic torque can be got in suitable condition of and D.B. Common-grounded drive schemeThe optical coupler drive scheme is most widespread used at present. The sampled current, speed and position signals transmit to the control part through optical couplers, and then the output signals pass through the optical coupler again and are amplified by drive part, last control the switches of the inverter. Isolation scheme is showed in fig.3. Optical coupler used in the system can cause time delay, even using high speed optical coupler the time delay is more than 2us. At the same time, because not every optical coupler has the same characteristic, the control signals can not be synchronous. Thus, the performance of system becomes worse. In this paper, common-grounded drive scheme is proposed. Optical couplers are not used between control part and drive part. Then time delay is reduced, so the dynamic and steady response characteristics of system are improved, and system cost is reduced. The common-grounded closed loop system is shown in Fig.4. The transfer function of system can be described as (10).Fig.3 Block Diagram of isolating driveFig.4 Block diagram of common-grounded drive F(S) = (10)Where, G(s) is the open loop transfer function. The drive system shown in Fig 3 can be described by transfer function (11)FG(S) = (11)Where, T1, T2 is the time delay in the main channel and feedback channel respectively.Fig.5 Contrast of step response between common-grounded drive and isolating driveSimulate the system according to (10) and (11) when both T1 and T2 are 2us. Simulation waveform is shown in Fig 5. Thus, system has better performance if the common ground strategy is used.Using both PWM_ON modulation and common-grounded drive scheme in the BLDCM system will reduce torque ripple, time delay, system fault and cost and so on.IV. PWM_ON COMMON-GROUNDED BLDCM SYSTEMThis part introduces the digital achievement of the proposed scheme based on FPGA chip. Digital BLDCM system consists of FPGA chip, drive circuit, three-phase inverter and BLDCM. The basic operating principle can be described as: position signals output from BLDCM input the decoder and position/velocity converter designed in FPGA, the error that velocity command subtracts the velocity feedback which is the output of position/velocity converter is amplified by PID regulator, and input PWM generator, position decoder output six 120 conducting signals according to position signals at the same time, PWM generator and decoder as an unit outputs six PWM_ON control signals; six control signals are amplified by drive circuit as the input of three-phase inverter, the six power switches operate PWM_ON state. The block chart of digital control system is showed in fig.6.Fig.6 Block diagram of converter systemPID algorithm is widely applied not only because its control structure is simple and its parameters is easily regulated, but it comprehends advantages of P regulator, I regulator and D regulator. The transfer function of PID algorithm in s-domain can be expressed as (12):HPID=KP(1+DS) (12)To be easily achieved by FPGA, (12) must be transformed into discrete form. (12) can be expressed by (13) which is in z-domain:HPID (z)= KP+(1-Z-1) (13)(13)can be discretized using difference equation (14):up(n)=Kpe(n) uI(n)=un-1+KI(en+en-1) (14)uD(n)=KD(en-en-1)The circuit structure of PID algorithm achieved by FPGA is showed in fig.7 according to (14).Fig.7 Hardware structure of PID algorithm achieved by FPGADrive circuit consists of IR2130 and relative peripheral circuit. IR2130 is key component to achieve common-grounded drive scheme. IR2130 has some good characteristics: it can drive three upper legs and three lower legs which bear high voltage; it can prevent cross-conduction because of under voltage and over-current shutdown; the most important is that it receives control signals and output to three-phase inverter directly without isolated component, so common-grounded scheme is achieved. Common-grounded drive simplifies circuit design, reduces signals delay and auxiliary power supplies. So the cost of BLDCM system is reduces.附录B公共接地无刷直流电机驱动系统的FPGA实现摘要提出了一种基于利用现场编程门阵列器进行控制的公共接地永磁无刷直流电机驱动系统。该系统具有两大特点:一是,前60的每个驱动滞后运用脉宽调制,后60不间断的进行脉宽调制(PWM);另一个是，控制电路与驱动电路之间没有光电耦合器进行电气隔离。所以,该系统具有一定的优势,比如降低了电磁转矩脉动、简化了的驱动电路使得信号的延迟变小、降低生产成本并且精简了大部分驱动系统。基于一个FPGA芯片设计了一个原型,并且利用该原型进行测试的实验结果证明了相关理论的正确性。关键词 公共接地驱动；无刷直流电机；现场可编程门阵列；PWM_ON调制策略第一章 引言由于无刷直流电动机具有效率高，功率密度高，良好的速度特性和简化控制等诸多优点，被广泛应用于现代控制系统。为了有效地控制无刷直流电动机系统，传统的无刷直流电机驱动方案是使用被光电耦合器隔离的控制电路输出的120 控制信号，提供给驱动电路并且控制电源主电路。因此，传统的无刷直流电机系统出现了一些缺点，如电磁转矩脉动大，体积大，成本高，和光耦合器造成的信号延迟等，这些缺点使传统的无刷直流电机系统不能应用在需要高精度，高稳定等条件的环境下。为了在一定程度上克服上述常规无刷直流电动机系统的缺点，本文提出了一种新的无刷直流电机系统，该系统应用PWM_ON调制策略和共同接地驱动器原理。设计的系统有两个特点：一是PWM_ON调制控制方式，在一个120 周期内，前60 的每个驱动器滞后适用脉宽调制(PWM)，而后者60 进行不间断脉宽调制;另一种是控制电路和驱动电路之间不存在用于电气隔离的光电耦合器。本文首先推导出了无刷直流电机的数学模型，然后分析了用于无刷直流电机系统的PWM_ON调制策略和共同接地驱动器的工作原理，对提出的设计原理进行仿真分析，最后，开发了基于FPGA芯片的120W无刷直流电机系统原型，并对实验结果进行分析。第二章 无刷直流电机的数学模型在近代，大多数基于主动控制的无刷直流电动机驱动器是由三相逆变电源提供无刷直流电机工作需要的方波的。本文接下来要推导的无刷直流电机的数学模型中包括三相逆变电源部分。无刷直流电机的数学模型由两部分组成，即机械方程和电压方程。本文在推导无刷直流电机的数学模型之前提出以下三个假设，具体如下：(1)三相定子绕组A ，B ，C的空间分布是均匀对称的，磁场的较高的谐波分量忽略不计。(2)磁饱和与铁芯损失（磁滞损耗，涡流损耗）是忽略不计的。(3)环境因素如温度，频率等电机的参数忽略不计。电机的机械运动方程是固定的，也不会随着坐标变换而改变。无刷直流电机的机械运动方程如下：Te Tl =J + B (1)TE是电磁转矩，负载转矩是TL， J是转子和负载惯量， B是摩擦系数,是无刷直流电机的转速。将三个阶段的定子电压作为状态变量。其电压平衡方程可以表示为(2):ua Ra ia La Lab Lac ia eaub = Rb ib + Lba Lb Lbc ib + eb (2)uc Rc ic Lca Lcb Lc ic ec 由于转子是永磁体，La ，Lb ，Lc ，Lab ，Lba ，Lac ，Lca ，Lbc ，Lcb ，可视为常数，那么，Ra=Rb=Rc=RsLa=Lb=Lc=L Lab=Lba=Lac=Lca=Lbc=Lcb=M (3)ia+ib+ic=0因此，我们得到了首相无刷直流电动机的电压方程，如(4)所示 ：Ua Rs ia LM ia ea Ub = Rs ib + LM ib + eb (4)Uc Rs ic LM ic ec无刷直流电机得拓扑模型是由(4)得到的，其模型如图1所示。图1 拓扑的无刷直流电机模型因此，无刷直流电机的数学模型可以由(1)和(4)描述。第三章 PWM_ON调制共同接地驱动架构作为三相逆变器而言， PWM控制方案被广泛应用于控制速度和目前的无刷直流电机控制系统。有以下常用的PWM调制模式： H_PWM L_ON，H_ONL_PWM和H_PWM L_PWM。前两种模式，实现起来非常简单，但缺点是，在每个电周期，相电流脉动都很大。最后一种模式为了具有减少电流脉动的优势而做了很多研究，但开关损耗过大。然而，应用于上述调制系统中的控制系统，其控制部分与驱动器部分是分离的。换句话说就是控制电路和驱动电路之间有起电气隔离作用的光学耦合器。光学耦合器肯定会产生信号迟延，从而降低系统特性。另一方面，这种方法会影响驱动器的可靠性同时提高生产成本。下面介绍 PWM_ON调制策略和共同接地控制方案。A： PWM_ON调制策略无刷直流电机的电路拓扑如图1所示。传统的控制方案是采用三相六拍和120度导电模式。不断产生电磁转矩，这就要求将理想梯形波在同一位置产生的电流反馈到EMF。不过，由于机绕组电感和可能会产生的转矩脉动，相电流的整流需要一定限度的时间。一些研究发现，转矩脉动的大小与非逆变整流电流有关，同时随调制方式的改变而改变。目前，几种主要的PWM调制有：上桥臂调制，下桥臂120度恒通(H_PWM);下桥臂调制，上桥臂120度恒通(L_PWM)，上下桥臂同时调制(H_PWM - L_PWM) ，头60度调制和后60度上下桥臂恒通（ PWM_ON ） ，头60度和后60度上下桥臂都调制等。研究表明，PWM_ON调制具有最小转矩脉动和开关损耗的优点。时序图如图2所示 。图2 PWM_ON控制信号时序电机的电磁转矩可用(5)表达 ：Te =(eaia+ebib+ecic) (5)其中，Te代表电磁转矩， P是磁极对， 代表电机转速，ea ,eb和 ec代表反馈电动势，ia, ib 和 ic代表三相电流。当电机运行常规控制方案斌且忽略相移的影响，电机的电磁转矩可表示为(6)：Te=2pkei (6)这里，Te代表电磁时间系数，i是稳定状态的电流。为了描述由pwm_on调制引起的相移而产生的转矩脉动，本文将以60 ，120 为例进行推导。如(7)所示的三相电流，可以获得建立无刷直流电机数学模型的依据。ia(t)=