Abstract:
An electromechanical actuator in a vehicle suspension system includes a housing having a first section adapted to affix to a vehicle body and a second section adapted to affix to a vehicle wheel assembly suspended to the vehicle body, the first and second sections coupled to form a motor, electronics including a power-switching devices disposed within a chamber of the housing and adapted to receive electrical power and to direct power to the motor, and a filter board including capacitors and inductors disposed within the chamber to suppress noise generated by the power-switching devices to an external DC power source.

Description:
TECHNICAL FIELD 
   This invention relates to an electromagnetic interference (EMI) filter. 
   BACKGROUND 
   Active automotive suspensions can include electrically powered actuators. In an active suspension system, power is supplied to the suspension, such as to help control vertical accelerations of a sprung mass when an unsprung mass encounters road disturbances. Integrating power electronics within an actuator can result in unacceptable levels of conducted electromagnetic interference (EMI). 
   SUMMARY 
   In one aspect, the invention features an electromechanical actuator including, in a vehicle suspension system, a housing having a first section adapted to affix to a vehicle body and a second section adapted to affix to a vehicle wheel assembly suspended to the vehicle body, the first and second sections coupled to form a motor, electronics including power-switching devices disposed within a chamber of the housing and adapted to receive electrical power and to direct power to the motor, and a filter board including capacitors and inductors disposed within the chamber to suppress electromagnetic emissions generated by the power-switching devices conducted to an external DC power source. 
   One or more of the following advantageous features can also be included. The motor can be a linear or rotary motor. The power-switching devices can be single-phase or multi-phase switching devices. The suppressed noise can be conducted emissions. The chamber can reduce radiated emissions from the power-switching devices. The DC power source can provide power which meets a variety of specifications such as having average voltage substantially equal to 325 volts, or greater than 12 volts, or greater than 42 volts, or greater than 118 volts, having peak current greater than 75 amps or substantially 100 amps, or having peak power substantially equal to or greater than 30 KW. The filter board can be designed to fit within a package having a predetermined volume, which can be less than 2,100,000 cubic millimeters. The capacitors can be non-electrolytic capacitors (ceramic and DC Film type) such as disk ceramics, monolithic/multilayer ceramics, polyester film, polycarbonate film, polypropylene film and metalized films, and so forth. The filter board can distribute capacitance while keeping line transients to a minimum. 
   In embodiments, the filter board can have an output impedance less than 1 ohm for frequencies within a 0 Hz to 2 kHz range. The filter board can have an output impedance less than 1 ohm for frequency within a 15 kHz to 5 MHz range. 
   In another aspect, the invention features an electromechanical actuator system including, in a vehicle suspension system, a housing having a first section adapted to affix to a vehicle body and a second section adapted to affix to a vehicle wheel assembly suspended to the vehicle body, the first and second sections coupled to form a motor, electronics including power-switching devices disposed within a chamber of the housing and adapted to receive electrical power and to direct power to the motor, and a filter board disposed within the chamber, the filter board including a multi-section ladder filter with dampening resistance designed for a package having a predetermined volume. 
   One or more of the following advantageous features can also be included. The motor can be a linear or rotary motor. The power-switching devices can be single-phase or multi-phase switching devices. The multi-section ladder filter can include capacitors and inductors. The multi-section ladder filter can include a dampening mechanism. The dampening mechanism can parallelly connect a resistance to at least one of the inductors. The dampening mechanism can serially connect a resistance to at least one of the capacitors. The multi-section ladder filter can include a dominant inductance serially connected to the power supply line. The dampening mechanism can parallelly connect a resistance to the dominant inductance to damp inductor-capacitor resonances that occur between the line inductance and a supply decoupling capacitance to protect the switching power devices and reduce the conducted and radiated EMI emissions. The dampening mechanism can also parallelly connect a link composed of a dampening resistance serially connected to a dampening capacitor, in parallel to at least one of the capacitors of the multi-section ladder filter. 
   In another aspect, the invention features an electromechanical actuator including, in a vehicle suspension system, a housing having a first section adapted to affix to a vehicle body and a second section adapted to affix to a vehicle wheel assembly suspended to the vehicle body, the first and second sections coupled to form a motor, electronics including power-switching devices disposed within a chamber of the housing and adapted to receive electrical power and to direct power to the motor, and a filter board disposed within the chamber and positioned between the power-switching devices and an external DC power source, the filter board cutoff frequency designed to facilitate the power-switching devices to switch at a predetermined switching frequency. 
   One or more of the following advantageous features can also be included. The motor can be a linear or rotary motor. The power-switching devices can be single-phase or multi-phase switching devices. The filter board can include capacitors and inductors. The predetermined switching frequency can be greater than audible frequencies such as 15 kilohertz (kHz). The capacitors and inductors can provide a predetermined attenuation to the power-switching devices output signals (and to the external DC power source signals) having frequency components greater than 520 kHz. The predetermined attenuation can be at least 120 decibels (dB). 
   In another aspect, the invention features an electromechanical actuator including, in a vehicle suspension system, a housing having a first section adapted to affix to a vehicle body and a second section adapted to affix to a vehicle wheel assembly suspended to the vehicle body, the first and second sections coupled to form a motor, electronics including power-switching devices disposed within a chamber of the housing and adapted to receive electrical power and to direct power to the motor, and a filter board disposed within the chamber and positioned between the power-switching devices and an external DC power source, the filter board designed to have specific vibration tolerance characteristics. 
   One or more of the following advantageous features can also be included. The motor can be a linear or rotary motor. The power-switching devices can be single-phase or multi-phase switching devices. The filter board can include capacitors and inductors. The vibration tolerance characteristics can follow Society of Automotive Engineers (SAE) J1211 recommendations. 
   In embodiments, the capacitors can be non-electrolytic capacitors (ceramic and DC Film type) such as disk ceramics, monolithic/multilayer ceramics, polyester film, polycarbonate film, polypropylene film and metalized films, and so forth. The filter board can distribute capacitance while keeping line transients to a minimum. 
   In another aspect, the invention features an electromechanical actuator including, in a vehicle suspension system, a housing having a first section adapted to affix to a vehicle body and a second section adapted to affix to a vehicle wheel assembly suspended to the vehicle body, the first and second sections coupled to form a motor, electronics including power-switching devices disposed within a chamber of the housing and adapted to receive electrical power and to direct power to the motor, and a filter board disposed within the chamber and positioned between the power-switching devices and an external DC power source, the filter board designed to meet specific EMI emissions specifications. 
   One or more of the following advantageous features can also be included. The motor can be a linear or rotary motor. The power-switching devices can be single-phase or multi-phase switching devices. The filter board can include capacitors and inductors. The specific EMI emissions specifications can be defined in Society of Automotive Engineers (SAE) J551 and J1113. 
   In embodiments, the capacitors can be non-electrolytic capacitors (ceramic and DC Film type) such as disk ceramics, monolithic/multilayer ceramics, polyester film, polycarbonate film, polypropylene film and metalized films, and so forth. The filter board can distribute capacitance while keeping line transients to a minimum. 
   In another aspect, the invention features an electromechanical actuator including, in a vehicle suspension system, a housing having a first section adapted to affix to a vehicle body and a second section adapted to affix to a vehicle wheel assembly suspended to the vehicle body, the first and second sections coupled to form a motor, electronics including power-switching devices disposed within a chamber of the housing and adapted to receive electrical power and to direct power to the motor, and a filter board with a power density of at least 0.0143 watts/cubic millimeter disposed within the chamber to suppress noise generated by the power-switching devices to an external DC power source. 
   One or more of the following advantageous features can also be included. The motor can be a linear or rotary motor. The power-switching devices can be single-phase or multi-phase switching devices. The suppressed noise can be conducted emissions. The filter board can include capacitors and inductors designed to fit within a package having a predetermined volume. The capacitors can be non-electrolytic capacitors (ceramic and DC Film type) such as disk ceramics, monolithic/multilayer ceramics, polyester film, polycarbonate film, polypropylene film and metalized films, and so forth. The filter board can distribute capacitance while keeping line transients to a minimum. 
   In another aspect, the invention features an electromechanical actuator including, in a vehicle suspension system, a housing having a first section adapted to affix to a vehicle body and a second section adapted to affix to a vehicle wheel assembly suspended to the vehicle body, the first and second sections coupled to form a motor, electronics including power-switching devices disposed within a chamber of the housing and adapted to receive electrical power and to direct power to the motor, and a filter board having a mass density substantially 0.0000007 kg per cubic millimeter disposed within the chamber to suppress noise generated by the power-switching devices to an external DC power source. 
   One or more of the following advantageous features can also be included. The motor can be a linear or rotary motor. The power-switching devices can be single-phase or multi-phase switching devices. The suppressed noise can be conducted emissions. The filter board can include capacitors and inductors designed to fit within a package having a predetermined volume. The capacitors can be non-electrolytic capacitors (ceramic and DC Film type) such as disk ceramics, monolithic/multilayer ceramics, polyester film, polycarbonate film, polypropylene film and metalized films, and so forth. The filter board can distribute capacitance while keeping line transients to a minimum. 
   In another aspect, the invention features an electromechanical actuator including, in a vehicle suspension system, a housing having a first section adapted to affix to a vehicle body and a second section adapted to affix to a vehicle wheel assembly suspended to the vehicle body, the first and second sections coupled to form a motor, electronics including power-switching devices disposed within a chamber of the housing and adapted to receive electrical power and to direct power to the motor, and a filter board disposed within the chamber, the filter board comprising a large inductor positioned between the external power supply and the power-switching devices by the power supply line. 
   One or more of the following advantageous features can also be included. The motor can be a linear or rotary motor. The power-switching devices can be single-phase or multi-phase switching devices. The large inductor can have dominant inductance relative to the power supply line. The large inductor can minimize the negative effects of the power line inductance to allow the power-switching devices to be located freely within the actuator. 
   Embodiments of the invention can have one or more of the following advantages. 
   A filter board, including capacitors and inductors, disposed within a chamber of an electromechanical actuator of an active vehicle suspension system, suppresses noise generated by power-switching devices to an external DC power source. 
   A filter board is disposed within a chamber of an electromechanical actuator in an active vehicle suspension system and is designed as a multi-section ladder filter with dampening resistance for a package having a predetermined volume. 
   A filter board is disposed within a chamber of an electromechanical actuator in an active vehicle suspension system and positioned between power-switching devices and an external DC power source, the filter board cutoff frequency is designed to facilitate the power-switching devices to switch at a predetermined switching frequency. 
   A filter board is disposed within a chamber of an electromechanical actuator in an active vehicle suspension system that follows specific vibration tolerance recommendations. 
   The filter board is designed to a specific power density for the power electronics within the active vehicle suspension system. 
   The filter board facilitates the integration of power electronics into an actuator. By doing so, besides cost and size benefits due to small packaging, switching phase currents are contained in a housing and travel along much shorter cables, thus reducing radiated EMI emissions. 
   The high order multi-section ladder EMI filter reduces the capacitance requirements and further facilitates packaging by allowing distribution of the capacitance while keeping line transients to a minimum and therefore minimizing conducted and radiated EMI emissions. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1  is a block diagram of a system. 
       FIG. 2  is a function diagram of the actuator of FIG.  1 . 
       FIG. 3  is a block diagram of the exemplary filter board of FIG.  2 . 
       FIG. 4  is a series of block diagrams showing a dampening resistor. 
     FIG.  5 ( a ) is the real part of the output impedance of the exemplary filter board. 
     FIG.  5 ( b ) is the magnitude of the current transfer function (frequency response) of the exemplary filter board. 
       FIG. 6  is an exemplary design of the multi-section filter board. 
       FIG. 7  is an exemplary layout of the integrated actuator. 
   

   DETAILED DESCRIPTION 
   In an active electromechanical suspension system, power is supplied to an electromechanical suspension to help control vertical accelerations of the sprung mass when the unsprung mass encounters road disturbances. The shock absorber of a common suspension can be replaced by a controlled force actuator that responds according to commands from a control system. The actuator can be electrically powered. High electrical current requirements for supplying the necessary power to an active vehicle suspension system can generate undesirable electromagnetic interference (EMI) that can interfere with radio reception and electrical devices in the vehicle. Further, packaging of an electrical actuator capable of developing the forces and speeds required to perform adequately as an active suspension actuator in the space available can be difficult. 
   In  FIG. 1 , a system  10  includes active vehicle suspension actuator  12 . The actuator  12  includes an armature  14  slidable with respect to a stator  16 . In this example, a linear motor configuration is utilized, but it should be understood that other types of motor configurations, such as a rotary motor, are also applicable. Stator  16  is attachable to an end of a top cap  18 , which is a metallic housing that defines an internal cavity and can have, for example, an oval cross section. Top cap  18  further affixes to a vehicle body  20 . Armature  14 , which affixes to a wheel assembly  22 , travels through this internal cavity as the armature  14  moves relative to the stator  16 . 
   Housed within the top cap  18  are on-board power electronics  24  and a filter board  26 . More specifically, power electronics  24  and filter board  26  are attached to top cap  18  and positioned inside top cap  18  in cavities defined by top cap  18  and armature  14  such that the power electronics  24  and filter board  26  do not interfere with armature  14  moving relative to stator  16 . The actuator  14  includes an electronic motor (armature  14  and stator  16 ) that converts electrical energy into mechanical work. The linear electronic motor, with appropriate communication controls, provides a controllable force between the wheel assembly  22  and the vehicle body  20 . Any variation in force that is desired can be produced by correspondingly varying a control signal. There are a variety of possible implementations for armature  14  and stator  16  such as those described in U.S. Pat. No. 5,574,445 (Maresca et al.) for a linear motor, incorporated herein by reference in its entirety. 
   In  FIG. 2 , a function block diagram  100  of the actuator  12  having integrated power electronics  24  and EMI (Electromagnetic Interference) filter board  26  is shown. A control signal  101 , such as an external analog or digital command signal from a central controller as shown or an internal control signal from the actuator  14  (not shown), is utilized to command the integrated actuator  12  to generate electrically controllable force between the sprung and unsprung masses. 
   Active suspension actuator  12  is electrically controlled by a processor  102 . Using a current controller  104 , the processor  102  commands single-phase or multiple-phase power-switching electronics  24 . The current controller  104  controls the phase currents that excite the linear motor (shown as actuator coils  108 ). For the illustrated three-phase power-switching electronics  24 , a basic function of the current controller  104  is to close a feedback loop in current for two of the phases and constrain the voltage of the third phase so that the internal neutral remains near zero voltage. The three-phase power-switching electronics  24  can be, for example, a BSM 150 GD 18 DLC manufactured by Eupec Corporation. The power electronics  24  contains power-switching devices that apply voltage to the actuator coils. Although the description below uses a three-phase power-switching module as an example, is not restricted to only three-phase power-switching modules and three-phase actuator topologies. It is applicable to single-phase or other multiple-phase power-switching modules and devices as well as other single-phase or multi-phase actuator topologies. 
   The actuator  12  includes multiple permanent magnets  110  (mounted on armature  14 ). The moving field is produced by the stator&#39;s  16  stationary windings (shown as actuator coils  108 ), whose three phases are commutated in the proper sequence. This sequence is governed by the position/velocity/acceleration of the magnets  110 . This information is provided by the position sensor  112 . 
   The functions of processor  102  and current controller  104  include deriving the proper switching logic sequence and commutation for the power-switching devices contained in power-switching module  24 . Ultimately the processor  102  provides a controllable force with respect to the position/velocity/acceleration of the actuator magnets  110  within its range of operation by providing current commands to the current controller  104 , which further controls the three-phase switching module  24  that creates individual phase currents to drive actuator coils  108 . The current sensors  107 - 1  and  107 - 2  are used to monitor the currents. The stator  16  (shown as actuator coils  108 ) interacts with armature  14  (shown as actuator magnets  110 ) to provide the desired force. To reduce radiated and conducted electromagnetic (EMI) emissions and to facilitate packaging of the power electronics  24  into the actuator  12 , the EMI filter board  26  is used between the external DC power line  114  and the power-switching module  24 . 
   Actuator  14  uses power whenever it generates force. The power is provided by one or more power sources including a generator, which can be used to provide power when actuator  14  operates under a low power condition. Additionally, a battery system and one or more energy storage devices, such as capacitors, can provide additional power when the actuator  14  operates under conditions that require higher power. The external power source can provide power which meets a variety of specifications, such as having average voltage substantially equal to 325 volts, or greater than 12 volts, or greater than 42 volts, or greater than 118 volts or having peak current greater than 75 amps or substantially 100 amps, or having peak power substantially equal to or greater than 30 KW, depending on the specific application requirements and power electronics  24  implementations. 
   Traditionally, a high-value capacitor, C, is used as a filter between the power supply  114  and the power-switching devices  24 . Capacitor values on the order of several thousand microfarads are typical. Since the power supply line  114  has some parasitic inductance, L, the high-value capacitor reduces the L-C resonance seen by the power-switching devices  24  and attenuates conducted EMI emissions. However, using a high-valued capacitor is problematic for at least two reasons. First, high-value, high-voltage capacitors are physically large. Therefore, it can be difficult, or impossible, to package the capacitor into the volume available in the actuator housing. Second, high-value capacitors are typically electrolytic-type, which have limited environmental capability, especially with respect to the vibration and temperature extremes required in an automotive application. 
   In  FIG. 3 , a schematic diagram  200  of the filter board  26  is shown. A power source  202  provides power to an integrated actuator  204  via power line wire  206 . The power source  202  can include a generator  208 , a battery system  210 , and one or more capacitors  212 . The cable wire  206  has line inductance value L-wire  214 . The filter board  26  is designed to meet a variety of specifications and constraints as described below. 
   The filter board  26  should provide a low impedance source (defined as: Z=(V 1 −V 2 )/I 2 , as labeled in  FIG. 3 , to the power-switching module  24 . A low impedance from the filter board  26  ensures that a substantial amount of the power transferred through the filter board  26  is delivered to the switching modules  24  and not dissipated in the filter  26  itself. 
   Depending on the specific application, the power-switching module  24 , which commands the motor  230 , can be designed to operate at different switching frequencies. For example, it can be desirable to switch at frequencies above the audible range, such as 15 to 20 KHz. 
   The filter board  26  reduces the conducted EMI emissions generated by the power-switching module  24  that are transmitted back onto the external power line  206 . The intensity of the EMI emissions is regulated by government agencies in many countries to prevent interference with other equipment. For an automotive application environment, SAE (Society of Automotive Engineers) EMC (Electromagnetic Compatibility) standards, such as SAE J551 and J1113, provide EMI specifications. By physically locating the power electronics  24  near the actuator coils  108  and within a metal actuator housing, the radiated EMI emissions from the actuator  14  are also reduced. 
   The filter board  26  also should suppress power supply transients entering from the power line  206  from affecting the power-switching module  24 . Without proper filtering, such transients can cause the power-switching module  24  to fail. 
   The filter board  26  and power electronics  24  combination should fit into the available space inside the actuator housing. For the exemplary actuator design as shown in  FIG. 2 , the space available inside the actuator housing for packaging board and power electronics combination can be less than 2,100,000 cubic millimeters (cm). The power density defined as peak power per cubic millimeter for the exemplary actuator with integrated filter board  26  and power electronics  24  is at least 0.0143 watts/cubic millimeter (30 KW/2100000 cubic millimeters). The mass density defined as kilograms of electronics per cubic millimeter is substantially 0.0000007 kg per cubic millimeter (1.5 kg mass/2100000 cubic millimeters). 
   To meet a variety of design specifications and constraints, as shown in  FIG. 3 , a multi-stage L-C (i.e., inductor-capacitor) filter ladder with damping resistor  216  is used. Since a single L-C section provides a second-order low pass filter effect, a higher-order multi-section ladder filter created by cascading several L-C sections together achieves significant attenuation (isolation) at the frequencies of interest. Thus, a conducted EMI emissions design requirement can be met. The order of a filter is the number of poles in the transfer function, which can be estimated from the number of reactive elements (capacitors and inductors) the filter contains. 
   The first stage of the filter  26  has a dominant inductor  218  (whose value is large relative to the power line inductance value L-wire  214 ) and a capacitor  220 . A damping resistor  216  is parallel-connected to the dominant inductor  218 . The remaining two stages include an inductor ( 226  for stage  2  and  228  for stage  3 ) and a capacitor ( 222  for stage  2  and  224  for stage  3 ). There are several advantages to this design. 
   The use of dominant inductor  218  in the first stage serves to minimize the sensitivity of the EMI filter  26  to power line inductance L-wire  214 . Minimizing the sensitivity to power line inductance allows the actuator to be located remotely from power supply  202  and eases the design constraint of power supply line length. 
   The use of several large-valued inductors ( 218 ,  226 , and  228 ) allows the design requirements to be met using a small amount of capacitance. Because only a small amount of capacitance is required, the physical space required by the capacitors is small. In turn, this makes the packaging of the power electronics  24  and filter board  26  into the actuator housing easier. In addition, the total capacitance is broken into three separate pieces, allowing the capacitance to more easily be physically distributed throughout the actuator housing. Because less capacitance is required, this design facilitates the utilization of smaller and more environmentally robust components (e.g., capacitors having better vibration and temperature tolerance as those recommended in SAE J1211 in an automotive application). 
   The use of a damping resistor  216  serves to reduce resonances in the filter  26 . A typical L-C section is an under-damped resonant circuit, which can lead to transient peaking at the power-switching module  24 . These transients can damage the power-switching module  24 , which makes damping necessary. Damping resistor  216  serves to damp these resonances, which causes conducted and radiated EMI emissions from the power electronics  24  and filter board  26  to be reduced. In addition, damping resistor  216  ensures that no damaging transients are presented to the power-switching module. 
   There are several ways for providing damping for a typical L-C section. In  FIG. 4 , (a) shows a damping resistor R parallel-connected to the inductor L, (b) shows a damping resistor R series-connected to the capacitor C. Other choices that can not be as efficient as (a) and (b) are shown in (c) where a damping resistor R is series-connected to the inductor L and (d) where a damping resistor R is parallel-connected to the capacitor C. As shown in  FIG. 3 , a damping resistance  216  is parallel-connected to the dominant inductor  218 . As discussed above, many other ways of providing damping can be implemented, such as to series or parallel-connect resistance to the inductors  226  or  228 , or to series or parallel-connect resistance to the capacitors  220 ,  222  and  224 . The dampening resistance can also be serially connected to a dampening capacitor to construct a link, the link further parallelly connected to at least one of the capacitors of the multi-section ladder filter. For this design, the capacitance of the dampening capacitor is smaller than the capacitance of the capacitors of the multi-section ladder filter. 
   Although circuit  26  shows three inductors  218 ,  226 ,  228  and three capacitors  220 ,  222 ,  224 , depending on system requirements, there can be more or less inductors and capacitors used. Thus, the order of the filter board  26  can be different. The combinations of the configurations discussed above in  FIG. 4  can also be used to provide damping. 
   In FIG.  5 ( a ) and FIG.  5 ( b ) an exemplary multi-section filter board  26  design is shown. The multi-section filter board  26  can be designed to meet a variety of specifications such as the attenuation for certain frequency ranges, cutoff frequencies, output impedance, damping function, and so forth, by properly choosing the design parameters such as the number of stages (the order of the filter board) and the values of the components (capacitors, inductors, resistors). Specifically, the inductor and capacitor values can be chosen such that the conducted EMI emissions meet the design specification as those defined in SAE J551 and J1113 and vibration tolerance characteristics follow those recommended in SAE J1211. Similarly, the inductor, capacitor, and resistor values can be chosen such that the output impedance of the filter is suitable for the power-switching module. 
   FIG.  5 ( a ) is the real part of the output impedance of the exemplary filter board (Re((V 1 −V 2 )/I 2 )) (as in FIG.  3 ), and FIG.  5 ( b ) is the magnitude of the current transfer function (frequency response) of the exemplary filter board (|I 2 /I 1 | as in FIG.  3 ). More specifically, as shown in FIG.  5 ( b ), certain high frequency ranges, such as those greater than 400 kHz, get a specific amount of attenuation, such as greater than 120 dB. 
   The output impedance of the filter board  26  is kept low to avoid unnecessary loss. In the example shown in FIG.  5 ( a ), a set of design specifications for the output impedance of the filter board  26  is such that the output impedance of the filter board  26  is less than 1 ohm during certain frequency ranges, such as for frequencies between 0 and 2 KHz and between 15 kHz and 5 MHz. This ensures that the filter  26  provides a low impedance source at those frequencies where significant power is delivered and at the switching frequency (and harmonics). 
   The actual inductors used to implement the filter  26  can be realized using combinations of series and parallel-connected inductors. Similarly, the actual capacitors used to implement the filter  26  can be realized using combinations of series and parallel-connected capacitors. Likewise, the actual resistors used to implement the filter  26  can be realized using combinations of series and parallel-connected resistors. 
   In  FIG. 6 , the multi-section filter board components that meet the filter design specifications as shown in FIG.  5 ( a ) and ( b ) are shown. Each inductor on the filter board is a 4.7 uH, 100 Amp inductor manufactured by Renco Electronics of Rockledge, Fla. The dominant inductor  218  includes four of these 4.7 uH inductors in series, to generate a total inductance of approximately 20 uH. Inductors  226  and  228  are each approximately 5.0 uH inductors. The parallel-connected resistor  216  is a 0.4 Ohm resistor. For power dissipation purposes, resistor  216  can be realized using multiple parallel-connected resistors. Capacitors  220 ,  222  and  224  include parallel-connected 1 uF, 400V capacitors manufactured by ITW Paktron of Bolingbrook, Ill. Three 1 uF parallel-connected capacitors make up the 3 uF capacitance of capacitors  220  and  222 . The 20 uF capacitance of capacitor  224  is made up of twenty 1 uF parallel-connected capacitors. 
   In  FIG. 7 , an exemplary layout  300  of the actuator  12  of  FIG. 1 , which further shows one possible layout of the power-switching module  24  and the filter board  26  within the actuator housing, is shown. The filter board  26 , located within the actuator top cap  18  as shown in  FIG. 1 , includes inductors  218 ,  226  and  228 , capacitors  220  and  222 , resistor  216 , and connects to the external DC power supply via the power supply line  206 . The filter board  26  further connects to the power-switching module  24  via the wires  330 . The processor  102 , current control circuit  104 , and power-switching module  24  are also located within the actuator top cap  18  (labeled as “Control Circuit” in FIG.  7 ). The capacitors ( 310 - 348 ) providing the capacitance  224  of the third stage of the multi-stage L-C filter ladder are physically located immediately above the power-switching module  24 .  FIG. 7  also shows the two current sensors  107 - 1  and  107 - 2  that connect to the actuator coils  108  within the stator  16 . The armature  14  having a number of magnets slides relative to the stator  16 . 
   A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.