diff --git a/docs/agents/hwp_pcu.rst b/docs/agents/hwp_pcu.rst
new file mode 100644
index 000000000..b1ff8b6c6
--- /dev/null
+++ b/docs/agents/hwp_pcu.rst
@@ -0,0 +1,87 @@
+.. highlight:: rst
+
+.. _hwp_pcu:
+
+=============
+HWP PCU Agent
+=============
+
+The HWP Phase Compensation Unit Agent interfaces with a 8 channel USB relay module
+(Numato Lab, product Number SKU:RL80001) to apply the discrete phase compensation in
+120-degree increments for the HWP motor drive circuit. When used in conjunction with
+a HWP pid controller, phase compensation in 60-degree increments can be achieved.
+
+.. argparse::
+    :filename: ../socs/agents/hwp_pcu/agent.py
+    :func: make_parser
+    :prog: python3 agent.py
+
+Configuration File Examples
+---------------------------
+
+Below are configuration examples for the ocs config file and for running the
+Agent in a docker container.
+
+OCS Site Config
+```````````````
+
+To configure your HWP PCU Agent for use with OCS you need to add a
+HWPPCUAgent block to your ocs configuration file. Here is an example
+configuration block that will automatically start data acquisition::
+
+  {'agent-class': 'HWPPCUAgent',
+   'instance-id': 'hwp-pcu',
+   'arguments': [['--port', '/dev/HWPPCU'],
+                 ['--mode', 'acq']]},
+
+Each device requires configuration under 'agent-instances'. See the OCS site
+configs documentation for more details.
+
+Docker Compose
+``````````````
+
+The HWP PCU Agent can (and probably should) be configured to run in a
+Docker container. An example configuration is::
+
+  ocs-hwp-pcu:
+    image: simonsobs/socs:latest
+    devices:
+      - "/dev/HWPPCU:/dev/HWPPCU"
+    hostname: nuc-docker
+    environment:
+      - INSTANCE_ID=hwp-pcu
+    volumes:
+      - ${OCS_CONFIG_DIR}:/config:ro
+
+The serial number will need to be updated in your configuration. The hostname
+should also match your configured host in your OCS configuration file. The
+site-hub and site-http need to point to your crossbar server, as described in
+the OCS documentation.
+
+
+Example Clients
+---------------
+
+To apply 120-degree phase compensation::
+
+    from ocs.matched_client import MatchedClient
+
+    hwp_pcu_client = MatchedClient("HWPPCU")
+
+    hwp_pcu_client.set_command(command='on_1')
+
+To apply 60 (= -120 + 180) degree phase compensation::
+
+    from ocs.matched_client import MatchedClient
+
+    hwp_pcu_client = MatchedClient("HWPPCU")
+    hwp_pid_client = MatchedClient("HWPPID")
+
+    hwp_pcu_client.set_command(command='on_2')
+    hwp_pid_client.set_direction(direction=1)
+
+Agent API
+---------
+
+.. autoclass:: socs.agents.hwp_pcu.agent.HWPPCUAgent
+    :members:
diff --git a/docs/index.rst b/docs/index.rst
index fb29de762..e75cae33f 100644
--- a/docs/index.rst
+++ b/docs/index.rst
@@ -45,6 +45,7 @@ API Reference        Full API documentation for core parts of the SOCS library.
     agents/generator
     agents/hwp_encoder
     agents/hwp_gripper
+    agents/hwp_pcu
     agents/hwp_picoscope
     agents/hwp_pid
     agents/hwp_pmx
diff --git a/socs/agents/hwp_pcu/__init__.py b/socs/agents/hwp_pcu/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/socs/agents/hwp_pcu/agent.py b/socs/agents/hwp_pcu/agent.py
new file mode 100644
index 000000000..0b9f220c7
--- /dev/null
+++ b/socs/agents/hwp_pcu/agent.py
@@ -0,0 +1,253 @@
+import argparse
+import time
+
+from ocs import ocs_agent, site_config
+from ocs.ocs_twisted import TimeoutLock
+from twisted.internet import reactor
+
+import socs.agents.hwp_pcu.drivers.hwp_pcu as pcu
+
+
+class HWPPCUAgent:
+    """Agent to phase compensation improve the CHWP motor efficiency
+
+    Args:
+        agent (ocs.ocs_agent.OCSAgent): Instantiated OCSAgent class for this agent
+        port (str): Path to USB device in '/dev/'
+
+    """
+
+    def __init__(self, agent, port):
+        self.agent: ocs_agent.OCSAgent = agent
+        self.log = agent.log
+        self.lock = TimeoutLock()
+        self.initialized = False
+        self.take_data = False
+        self.port = port
+        self.status = 'off'
+
+        agg_params = {'frame_length': 60}
+        self.agent.register_feed(
+            'hwppcu', record=True, agg_params=agg_params)
+
+    @ocs_agent.param('auto_acquire', default=False, type=bool)
+    @ocs_agent.param('force', default=False, type=bool)
+    def init_connection(self, session, params):
+        """init_connection(auto_acquire=False, force=False)
+
+        **Task** - Initialize connection to PCU
+        Controller.
+
+        Parameters:
+            auto_acquire (bool, optional): Default is False. Starts data
+                acquisition after initialization if True.
+            force (bool, optional): Force initialization, even if already
+                initialized. Defaults to False.
+
+        """
+        if self.initialized and not params['force']:
+            self.log.info("Connection already initialized. Returning...")
+            return True, "Connection already initialized"
+
+        with self.lock.acquire_timeout(3, job='init_connection') as acquired:
+            if not acquired:
+                self.log.warn(
+                    'Could not run init_connection because {} is already running'.format(self.lock.job))
+                return False, 'Could not acquire lock'
+
+            try:
+                self.PCU = pcu.PCU(port=self.port)
+                self.log.info('Connected to PCU')
+            except BrokenPipeError:
+                self.log.error('Could not establish connection to PCU')
+                reactor.callFromThread(reactor.stop)
+                return False, 'Unable to connect to PCU'
+
+        self.status = self.PCU.get_status()
+        self.initialized = True
+
+        # Start 'acq' Process if requested
+        if params['auto_acquire']:
+            self.agent.start('acq')
+
+        return True, 'Connection to PCU established'
+
+    @ocs_agent.param('command', default='off', type=str, choices=['off', 'on_1', 'on_2', 'hold'])
+    def send_command(self, session, params):
+        """send_command(command)
+
+        **Task** - Send commands to the phase compensation unit.
+        off: The compensation phase is zero.
+        on_1: The compensation phase is +120 deg.
+        on_2: The compensation phase is -120 deg.
+        hold: Stop the HWP spin.
+
+        Parameters:
+            command (str): set the operation mode from 'off', 'on_1', 'on_2' or 'hold'.
+
+        """
+        with self.lock.acquire_timeout(3, job='send_command') as acquired:
+            if not acquired:
+                self.log.warn('Could not send command because {} is already running'.format(self.lock.job))
+                return False, 'Could not acquire lock'
+
+            command = params['command']
+            if command == 'off':
+                off_channel = [0, 1, 2, 5, 6, 7]
+                for i in off_channel:
+                    self.PCU.relay_off(i)
+                self.status = 'off'
+                return True, 'Phase compensation is "off".'
+
+            elif command == 'on_1':
+                on_channel = [0, 1, 2]
+                off_channel = [5, 6, 7]
+                for i in on_channel:
+                    self.PCU.relay_on(i)
+                for i in off_channel:
+                    self.PCU.relay_off(i)
+                self.status = 'on_1'
+                return True, 'Phase compensation operates "on_1".'
+
+            elif command == 'on_2':
+                on_channel = [0, 1, 2, 5, 6, 7]
+                for i in on_channel:
+                    self.PCU.relay_on(i)
+                self.status = 'on_2'
+                return True, 'Phase compensation operates "on_2".'
+
+            elif command == 'hold':
+                on_channel = [0, 1, 2, 5]
+                off_channel = [6, 7]
+                for i in on_channel:
+                    self.PCU.relay_on(i)
+                for i in off_channel:
+                    self.PCU.relay_off(i)
+                self.status = 'hold'
+                return True, 'Phase compensation operates "hold".'
+
+            else:
+                return True, "Choose the command from 'off', 'on_1', 'on_2' and 'hold'."
+
+    def get_status(self, session, params):
+        """get_status()
+
+        **Task** - Return the status of the PCU.
+
+        """
+        with self.lock.acquire_timeout(3, job='get_status') as acquired:
+            if not acquired:
+                self.log.warn(
+                    'Could not get status because {} is already running'.format(self.lock.job))
+                return False, 'Could not acquire lock'
+
+            self.status = self.PCU.get_status()
+
+        return True, 'Current status is ' + self.status
+
+    def acq(self, session, params):
+        """acq()
+
+        **Process** - Start PCU data acquisition.
+
+        Notes:
+            The most recent data collected is stored in the session data in the
+            structure::
+
+                >>> response.session['data']
+                {'status': 'on_1',
+                 'last_updated': 1649085992.719602}
+
+        """
+        with self.lock.acquire_timeout(timeout=3, job='acq') as acquired:
+            if not acquired:
+                self.log.warn('Could not start pcu acq because {} is already running'
+                              .format(self.lock.job))
+                return False, 'Could not acquire lock'
+
+            session.set_status('running')
+            last_release = time.time()
+            self.take_data = True
+
+            while self.take_data:
+                # Relinquish sampling lock occasionally.
+                if time.time() - last_release > 1.:
+                    last_release = time.time()
+                    if not self.lock.release_and_acquire(timeout=10):
+                        self.log.warn(f"Failed to re-acquire sampling lock, "
+                                      f"currently held by {self.lock.job}.")
+                        continue
+
+                data = {'timestamp': time.time(),
+                        'block_name': 'hwppcu', 'data': {}}
+
+                # status = self.PCU.get_status()
+                status = self.status
+                data['data']['status'] = status
+
+                self.agent.publish_to_feed('hwppcu', data)
+
+                session.data = {'status': status,
+                                'last_updated': time.time()}
+
+                time.sleep(5)
+
+        self.agent.feeds['hwppcu'].flush_buffer()
+        return True, 'Acqusition exited cleanly'
+
+    def _stop_acq(self, session, params):
+        """
+        Stop acq process.
+        """
+        if self.take_data:
+            self.PCU.close()
+            self.take_data = False
+            return True, 'requested to stop taking data'
+
+        return False, 'acq is not currently running'
+
+
+def make_parser(parser=None):
+    """
+    Build the argument parser for the Agent. Allows sphinx to automatically build documentation
+    baised on this function
+    """
+    if parser is None:
+        parser = argparse.ArgumentParser()
+
+    # Add options specific to this agent
+    pgroup = parser.add_argument_group('Agent Options')
+    pgroup.add_argument('--port', type=str, help="Path to USB node for the lakeshore")
+    pgroup.add_argument('--mode', type=str, default='acq',
+                        choices=['init', 'acq'],
+                        help="Starting operation for the Agent.")
+    return parser
+
+
+def main(args=None):
+    parser = make_parser()
+    args = site_config.parse_args(agent_class='HWPPCUAgent',
+                                  parser=parser,
+                                  args=args)
+
+    init_params = False
+    if args.mode == 'init':
+        init_params = {'auto_acquire': False}
+    elif args.mode == 'acq':
+        init_params = {'auto_acquire': True}
+
+    agent, runner = ocs_agent.init_site_agent(args)
+    hwppcu_agent = HWPPCUAgent(agent,
+                               port=args.port)
+    agent.register_task('init_connection', hwppcu_agent.init_connection,
+                        startup=init_params)
+    agent.register_process('acq', hwppcu_agent.acq,
+                           hwppcu_agent._stop_acq)
+    agent.register_task('send_command', hwppcu_agent.send_command)
+    agent.register_task('get_status', hwppcu_agent.get_status)
+
+    runner.run(agent, auto_reconnect=True)
+
+
+if __name__ == '__main__':
+    main()
diff --git a/socs/agents/hwp_pcu/drivers/__init__.py b/socs/agents/hwp_pcu/drivers/__init__.py
new file mode 100644
index 000000000..e69de29bb
diff --git a/socs/agents/hwp_pcu/drivers/hwp_pcu.py b/socs/agents/hwp_pcu/drivers/hwp_pcu.py
new file mode 100644
index 000000000..7ea7e58d6
--- /dev/null
+++ b/socs/agents/hwp_pcu/drivers/hwp_pcu.py
@@ -0,0 +1,73 @@
+import time
+
+import serial
+
+
+class PCU:
+    """Class to communicate with the phase compensation unit.
+
+    Args:
+        port (str): Path to USB device in '/dev/'
+
+    Attributes:
+        status (str): The status of the unit (off/on_1/on_2/hold)
+    """
+
+    def __init__(self, port):
+        self.port = serial.Serial(
+            port,
+            baudrate=19200,
+            timeout=10,
+        )
+
+    def close(self):
+        self.port.close()
+
+    def relay_on(self, channel):
+        cmd = "relay on " + str(channel) + "\n\r"
+        self.port.write(cmd.encode('utf-8'))
+        time.sleep(.1)
+
+    def relay_off(self, channel):
+        cmd = "relay off " + str(channel) + "\n\r"
+        self.port.write(cmd.encode('utf-8'))
+        time.sleep(.1)
+
+    def relay_read(self, channel):
+        cmd = "relay read " + str(channel) + "\n\r"
+        self.port.write(cmd.encode('utf-8'))
+        time.sleep(.1)
+        response = self.port.read(25)
+        time.sleep(.1)
+        response = response.decode('utf-8')
+        if response.find("on") > 0:
+            return True
+        elif response.find("off") > 0:
+            return False
+        else:
+            return -1
+
+    def get_status(self):
+        """get_status()
+
+        **Task** - Get the operation mode of the phase compensation unit.
+        off: The compensation phase is zero.
+        on_1: The compensation phase is +120 deg.
+        on_2: The compensation phase is -120 deg.
+        hold: Stop the HWP spin.
+        """
+        channel = [0, 1, 2, 5, 6, 7]
+        channel_switch = []
+
+        for i in channel:
+            channel_switch.append(self.relay_read(i))
+        if channel_switch == [False, False, False, False, False, False]:
+            return 'off'
+        elif channel_switch == [True, True, True, False, False, False]:
+            return 'on_1'
+        elif channel_switch == [True, True, True, True, True, True]:
+            return 'on_2'
+        elif channel_switch == [True, True, True, True, False, False]:
+            return 'hold'
+        else:
+            return 'undefined'